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How to use double-angle identities

CC.HSF.TF.A.1

auto-gen

Converting between degrees and radians

Trigonometric ratios of angles in radians

Radian measure and arc length

CC.HSF.TF.A.2

Unit circle

CC.HSF.TF.A.3

Solving expressions using 45-45-90 special right triangles

Solving expressions using 30-60-90 special right triangles

Find the exact value of trigonometric ratios

CC.HSF.TF.B.5

Graphing transformations of trigonometric functions

Determining trigonometric functions given their graphs

CC.HSF.TF.B.6

Find the difference of squares: (a - b)(a + b) = (a^2 - b^2)

Find the difference of squares

Solving two-step linear equations using addition and subtraction: ax + b = c

Two-step Linear Equations

Two-step Linear Equations LHS

Solve Linear Equations Using Addition and Subtraction – Word Problem

Two-step Linear Equations — Word Problem

CC.HSF.TF.B.7

Evaluating inverse trigonometric functions

CC.HSF.TF.C.8

Pythagorean identities

CC.HSF.TF.C.9

Sum and difference identities

Sum and Difference Identities

Double-angle identities

Cofunction identities

CC.HSG.C.B.5

CC.HSG.CO.A.1

Line symmetry

Angles in a circle

Chord properties

Circles and circumference

Circle properties

Parallel and perpendicular line segments

Identifying Parallel Lines

Identifying Perpendicular Lines

CC.HSG.SRT.C.6

Use sine ratio to calculate angles and sides (Sin = o / h)

Use tangent ratio to calculate angles and sides (Tan = o / a)

CC.HSG.SRT.C.7

Use cosine ratio to calculate angles and sides (Cos = a / h)

CC.HSG.SRT.C.8

Combination of SohCahToa questions

Word problems relating ladder in trigonometry

Word problems relating guy wire in trigonometry

CC.HSG.SRT.D.10

Law of sines

Ambiguous case: SSA triangles

Law of cosines

CC.HSG.SRT.D.11

Applications of the sine law and cosine law

CC.HSG.SRT.D.9

Area of triangles: 1/2 a*b sin(C)

math

Ex. 1:

Ex. 2:

Ex. 3:

In this lesson, we will learn how to make use of the double-angle identities, a.k.a. double-angle formulas to find the sine and cosine of a double angle. It's hard to simplify complex trigonometric functions without these formulas. 

Use sine ratio to calculate angles and sides (Sin = \(  \frac{o}{h}\) )

Use cosine ratio to calculate angles and sides (Cos =  \(  \frac{a}{h}\)  )

Use tangent ratio to calculate angles and sides (Tan =  \(  \frac{o}{a}\)  )