Question 1
Given sinx=53, find cosx.
Step 1: Start with the Pythagorean identity.
sin2x+cos2x=1
Step 2: Substitute the given value.
(53)2+cos2x=1
259+cos2x=1
Step 3: Isolate cos2x.
cos2x=1−259=2516
Step 4: Take the square root (principal value for acute angle).
cosx=±54
Assuming x is acute, cosx=54.
cosx=54
Question 2
Given cosx=54, find sinx.
Step 1: Start with the Pythagorean identity.
sin2x+cos2x=1
Step 2: Substitute the given value.
sin2x+(54)2=1
sin2x+2516=1
Step 3: Isolate sin2x.
sin2x=1−2516=259
Step 4: Take the square root (principal value for acute angle).
sinx=±53
Assuming x is acute, sinx=53.
sinx=53
Question 4.1
Simplify sin(90∘−θ).
Step 1: In a right triangle, sin(90∘−θ) is opposite over hypotenuse for angle (90∘−θ).
The opposite side to (90∘−θ) is the adjacent side to θ.
Step 2: Thus, sin(90∘−θ)=hypotenuseadjacenttoθ=cosθ.
sin(90∘−θ)=cosθ
Question 4.2
Simplify cos(90∘−θ).
Step 1: cos(90∘−θ) is adjacent over hypotenuse for angle (90∘−θ).
The adjacent side to (90∘−θ) is the opposite side to θ.
Step 2: Thus, cos(90∘−θ)=hypotenuseoppositetoθ=sinθ.
cos(90∘−θ)=sinθ
Question 4.3
Simplify tan(90∘−θ).
Step 1: tan(90∘−θ)=adjacentto(90∘−θ)oppositeto(90∘−θ).
Step 2: Opposite to (90∘−θ) is adjacent to θ, adjacent to (90∘−θ) is opposite to θ.
Step 3: Thus, tan(90∘−θ)=oppositetoθadjacenttoθ=cotθ.
tan(90∘−θ)=cotθ
Question 4.4
Prove sin2θ+cos2θ=1 using the right triangle.
Step 1: Label the right triangle with hypotenuse r, opposite side to θ is y, adjacent side is x.
sinθ=ry,cosθ=rx
Step 2: By Pythagorean theorem in the triangle,
r2=x2+y2
Step 3: Divide both sides by r2.
r2r2=r2x2+r2y2
1=cos2θ+sin2θ
sin2θ+cos2θ=1