Answer:
D. Pythagorean
Step-by-step explanation:
Given the identity
cos²x - sin²x = 2 cos²x - 1.
To show that the identity is true, we need to show that the left hand side is equal to right hand side or vice versa.
Starting from the left hand side
cos²x - sin²x ... 1
According to Pythagoras theorem, we know that x²+y² = r² in a right angled triangle. Coverting this to polar form, we have:
x = rcostheta
y = rsintheta
Substituting into the Pythagoras firnuka we have
(rcostheta)²+(rsintheta)² = r²
r²cos²theta+r²sin²theta = r²
r²(cos²theta+sin²theta) = r²
(cos²theta+sin²theta) = 1
sin²theta = 1 - cos²theta
sin²x = 1-cos²x ... 2
Substituting equation 2 into 1 we have;
= cos²x-(1-cos²x)
= cos²x-1+cos²x
= 2cos²x-1 (RHS)
This shows that cos²x -sin²x = 2cos²x-1 with the aid of PYTHAGORAS THEOREM
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Four? Isn't it stated in the question? Unless I am assuming wrong.
Algebra is number 3 - You have subtracted the measure of angle HKI from the equation.
Transitive property of equality is number 2 - Because both pairs of angles equal 180 degrees, you can set them equal to each other.
Definition of congruence is number 4 - The congruence symbol is in the equation, which tells you that the two angles are congruent.
Angles forming a linear pair sum to 180 degrees is number 1 - 180 degrees is in the equations given and the angles all form linear pairs.
Hope this helps!! :)
