Is cos^2(90)-sin^2(90)=cos(180) ?

The answer to whether cos^2(90)-sin^2(90)=cos(180) is True

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prove cos^2(90)-sin^2(90)=cos(180)

prove

cos^{2} (9 0^{\circ}) - sin^{2} (9 0^{\circ}) = cos (18 0^{\circ})

True

Solution steps

cos^{2} (9 0^{\circ}) - sin^{2} (9 0^{\circ}) = cos (18 0^{\circ})

Manipulating left side

cos^{2} (9 0^{\circ}) - sin^{2} (9 0^{\circ})

Simplify

cos^{2} (9 0^{\circ}) - sin^{2} (9 0^{\circ}) : - 1

= - 1

Manipulating right side

cos (18 0^{\circ})

Simplify

= - 1

We showed that the two sides could take the same form

\Rightarrow True

1 - sin (r) = cos (r)

sin (1 5^{\circ}) = \frac{1 - cos ( 3 0 ^{\circ} )}{2}

sin (- 1) = - sin (1)

tan (x) cot (x) = sin^{2} (x) + cos^{2} (x)

\frac{( csc ^{2} ( x ) )}{1 + tan ^{2} ( x )} = cot^{2} (x)

Is cos^2(90)-sin^2(90)=cos(180) ?
The answer to whether cos^2(90)-sin^2(90)=cos(180) is True