Thursday, August 08, 2024

Orphaned Strategies

This post is intended as a home for useful but orphaned math strategies. Included are Triangles Within Triangles, Avoid Fractions on the SAT/ACT, and Two Reactions to Right Triangles.

Proceed to peruse these and other SAT/ACT math and general approach tips.

[Note: “iff” means “if and only if.”] 

Triangles Within Triangles 

On the SAT, whenever a triangle appears inside another triangle, all triangles will be similar, and setting up and solving a proportion will solve the given problem.

Avoid Fractions on the SAT/ACT

It’s often best to entirely avoid fractions on the SAT/ACT. Instead, fractions can be converted to decimals to make numbers more intuitive and calculations, estimates, and comparisons easier.

Two Reactions to Right Triangles

Whenever encountering a right triangle in a math problem, immediately ask two questions: Could I use the Pythagorean theorem? Could I use SOH CAH TOA? Nine times out of ten one of those approaches will lead to the solution.

No Solutions

Questions referencing equations or systems with “no solutions” are common on the SAT/ACT math tests. They mainly come in two flavors: quadratic equations, and linear/non-linear systems.

SAT/ACT questions involving quadratic equations with no solutions can be solved using the Discriminant: D = b^2–4ac. There are no real solutions to a quadratic equation iff D < 0, and this inequality will usually solve the given problem.

In general, linear or non-linear systems with no solution produce graphs with no points of intersection. Linear systems have no solutions iff the lines graphed are parallel iff slopes are equal. Desmos can be employed to draw the graphs of both equations, and see what needs to be done (e.g. with sliders) to ensure required conditions are met.

40 Top Tips for Taking Standardized Tests

Click here to read my collected musings and battle-tested general approach tips for improving scores on standardized assessments like the SAT and ACT.

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Copyright © 2006-present: Christopher R. Borland. All rights reserved.

Thursday, August 01, 2024

Analytic Geometry – What You Need to Know

Analytic geometry is a core sub-topic in all algebra courses, blending geometry and algebra on a coordinate grid measured by x and y axes. 

As the story goes, famous French polymath René Descartes came up with the idea after watching a fly crawl up a wall.

These questions comprise a large fraction of SAT/ACT questions, and students must fully command key elements.

Following is what you need to know. 

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Equation of a line 
y = mx+b.
m = slope, b = y-intercept.

Equation of a parabola
Vertex form: y = a(x-h)^2 + k, vertex is (h,k).
Standard form: y = ax^2+bx+c, vertex is (h,k) with h = -b/2a, k = f(h).

Equation of a circle
(x-h)^2+(y-k)^2 = r^2.
Vertex is (h,k), radius = r.

To write the equation of a line containing 2 given points (x,y):
Use a Desmos table together with y1 ~ mx1+b to return m, b.

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For practice, search Google for worksheets covering any or all of the above, pick a worksheet that provides answers, complete the worksheet, analyze any mistakes, and redo it until you can complete that worksheet with no errors. Then repeat, with additional worksheets, as needed, until you’ve mastered this material.

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Copyright © 2006-present: Christopher R. Borland. All rights reserved.

Monday, July 08, 2024

Geometry Hacks

Did you know you can use a ruler, protractor, and straight-edge on the SAT/ACT? 

Actually you can’t, at least not prohibited plastic or metal ones. 

"Too bad," you might be thinking. It would make answering most geometry questions a whole lot easier.

But you can easily and legally improvise each of these tools with materials you're allowed to use on the SAT/ACT. 

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Ruler

Along the edge of your scratch paper, mark the endpoints of a segment of known length taken from the given figure. Add a mark in the middle, to indicate the half-way point. Knowing the overall length of this “ruler,” and the length of the half-way mark, you can lay the ruler over the segment you need to find in the figure (on screen or on paper) to closely guess its length. Now, eliminate answers, and choose the best one remaining.

Protractor

You can create a “protractor” by using the right angle at any corner of your scratch paper. Carefully fold your scratch paper edge-to-edge at the corner. This forms a perfect 45 degree angle. Fold it again, like you’re making a paper airplane. Unfold and flatten the page. The angles formed are 22.5 degrees each. You’ve now created a “protractor” with angles 22.5 degrees, 45 degrees, 67.5 degrees and 90 degrees.

Straight-Edge

The edge of a sharply-folded scratch page makes an excellent edge for quickly drawing perfectly straight lines. In mathematics, neatness matters, nowhere more so than in the realm of geometry.

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Note: 

To form nice, sharp edges, run your pen or pencil firmly across the folds as you create each crease.

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Copyright © 2006-present: Christopher R. Borland. All rights reserved.

Monday, July 01, 2024

The New Online ACT

It had to happen. Following the lead of the SAT, the ACT has been streamlined and is now offered online.

In its new format, the ACT takes less time to complete (only 125 minutes), there are fewer questions in each section (with more time per question), math questions have only four answer choices instead of five, English and Reading passages are shorter, and the science section is optional.

Beginning in April 2025, students can choose to take the ACT on paper or online. The new format will be introduced in April 2025 for online ACT tests only. From September 2025 forward, all ACTs will be given in the new format.

Click here for complete official information about recent changes to the ACT.

ACT now provides students with practice in the new digital format. Unfortunately, only a single official full-length online ACT practice test is offered, separated into section tests (English, Mathematics, Reading, Science).

To find the sample test, go to ACT Official Online Practice Tests, and click the button near the bottom marked "Launch ACT Free Online Tests" (you'll first need to create a MyACT account). 

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Copyright © 2006-present: Christopher R. Borland. All rights reserved.

Saturday, June 08, 2024

The Backdoor

To enter, if the front door's open, walk right in. If it’s not, go ‘round back. This common sense advice applies to the SAT/ACT math section, as well.

While “doing the math” should always be plan A, plan B is to use a strategy, a “backdoor” approach to selecting the right answer. If the math is easy, do the math. If not, use a strategy!

Following are two classic backdoor strategies for answering questions on multiple-choice math questions. Each of them takes practice to master, but the advantage gained is well worth the effort. 

Try the answers

Math problems are typically solved by working forward from given information to the answer. This approach is the only option on typical “fill in the blank” tests taken in school, and on the SAT and ACT, students are expected to employ the same approach. But on multiple-choice tests, students have another option: it might be better to work backwards, from the answers to the problem. If answer are all numerals, this a good strategy to consider. 

Here's how it works:

Pick an answer choice. Take that answer back into the question and see if it’s consistent with all the given information. If there’s any inconsistency, eliminate that one, and try another. Only the correct answer will work. 

This strategy works best when answer choices are all numerals.

[Note: Since answers are arranged numerically, starting your search in the middle of the list will enable faster elimination and likely save time.]

Make up numbers

If variables are confusing you, don’t use variables. Use simple, real numbers instead! Here's how it works:

Pick simple sample values for the unknowns (don’t use 1, 0, or any number already appearing in the question), and answer the question using those numbers. Plug the same values into the answers, and pick the one that gives you the same result.

This approach works best when solving algebra problems and you're tempted to write some kind of difficult equation and/or when the answers all contain variables.

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Copyright © 2006-present: Christopher R. Borland. All rights reserved.