Is cos(pi-t)=-cos(t) ?

The answer to whether cos(pi-t)=-cos(t) is True

English

Español

Português

Français

Deutsch

Italiano

Русский

中文(简体)

한국어

日本語

Tiếng Việt

עברית

العربية

prove cos(pi-t)=-cos(t)

prove

cos (π - t) = - cos (t)

True

Solution steps

cos (π - t) = - cos (t)

Manipulating left side

cos (π - t)

Rewrite using trig identities

cos (π - t)

Use the Angle Difference identity:

cos (s - t) = cos (s) cos (t) + sin (s) sin (t)

= cos (π) cos (t) + sin (π) sin (t)

Simplify

cos (π) cos (t) + sin (π) sin (t) : - cos (t)

cos (π) cos (t) + sin (π) sin (t)

cos (π) cos (t) = - cos (t)

cos (π) cos (t)

Simplify

cos (π) : - 1

cos (π)

Use the following trivial identity:

cos (π) = (- 1)

cos (x)

periodicity table with

2 πn

cycle:

x 0 \frac{π}{6} \frac{π}{4} \frac{π}{3} \frac{π}{2} \frac{2 π}{3} \frac{3 π}{4} \frac{5 π}{6} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} x π \frac{7 π}{6} \frac{5 π}{4} \frac{4 π}{3} \frac{3 π}{2} \frac{5 π}{3} \frac{7 π}{4} \frac{11 π}{6} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

= - 1

= - 1 \cdot cos (t)

Multiply:

1 \cdot cos (t) = cos (t)

= - cos (t)

= - cos (t) + sin (π) sin (t)

sin (π) sin (t) = 0

sin (π) sin (t)

Simplify

sin (π) : 0

sin (π)

Use the following trivial identity:

sin (π) = 0

sin (x)

periodicity table with

2 πn

cycle:

x 0 \frac{π}{6} \frac{π}{4} \frac{π}{3} \frac{π}{2} \frac{2 π}{3} \frac{3 π}{4} \frac{5 π}{6} sin (x) 0 \frac{1}{2} \frac{2}{2} \frac{3}{2} 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} x π \frac{7 π}{6} \frac{5 π}{4} \frac{4 π}{3} \frac{3 π}{2} \frac{5 π}{3} \frac{7 π}{4} \frac{11 π}{6} sin (x) 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2}

= 0

= 0 \cdot sin (t)

Apply rule

0 \cdot a = 0

= 0

= - cos (t) + 0

- cos (t) + 0 = - cos (t)

= - cos (t)

= - cos (t)

= - cos (t)

We showed that the two sides could take the same form

\Rightarrow True