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.