SAT Math Formulas: What to Memorize and What's Given

The digital SAT provides a reference sheet with common geometry formulas, including areas, volumes and special right triangles. It doesn't give you most of the algebra. Those are the ones to learn.

Lines

m = \frac{y _{2} - y _{1}}{x _{2} - x _{1}} y = m x + b

Parallel lines have equal slopes, and perpendicular slopes are negative reciprocals.

Quadratics

x = \frac{- b \pm b ^{2} - 4 a c}{2 a}

The vertex's $x$ is $- \frac{b}{2 a}$ . The discriminant, $b^{2} - 4 a c$ , tells you the number of real solutions. Also know that the sum of the solutions is $- \frac{b}{a}$ and the product is $\frac{c}{a}$ .

Exponents and growth

y = a (1 + r)^{t} y = a (1 - r)^{t}

Each percent change becomes a multiplier. Up 6% is $1.06$ , and down 6% is $0.94$ .

Percent and data

percent change = \frac{new - old}{old} \times 100

The mean is the total divided by the count, and the median is the middle after sorting.

Circles

(x - h)^{2} + (y - k)^{2} = r^{2}

The equation of a circle isn't on the reference sheet. Know how to read the center and the radius, and how to complete the square.

Trig

Know SOH CAH TOA, and that $sin A = cos (9 0^{\circ} - A)$ . That relationship comes up often.

Watch out for this

Spending your time on formulas the test gives you.

Use the sheet for geometry, and save your memory for algebra. Knowing when to use a formula matters more than reciting it.

Want to check your work? Open the free calculator

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