What is the value of cos(155)cos(20)+sin(155)sin(20) ?

The value of cos(155)cos(20)+sin(155)sin(20) is -(sqrt(2))/2

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cos(155)cos(20)+sin(155)sin(20)

cos (15 5^{\circ}) cos (2 0^{\circ}) + sin (15 5^{\circ}) sin (2 0^{\circ})

- \frac{2}{2}

Solution steps

cos (15 5^{\circ}) cos (2 0^{\circ}) + sin (15 5^{\circ}) sin (2 0^{\circ})

Rewrite using trig identities:

cos (13 5^{\circ})

= cos (13 5^{\circ})

Use the following trivial identity:

cos (13 5^{\circ}) = - \frac{2}{2}

= - \frac{2}{2}

sin (3) (\frac{π}{2})

sin (0.02)

2 cos (- \frac{π}{4})

2 cos (- \frac{π}{3})

25 \cdot cos (4 5^{\circ})

What is the value of cos(155)cos(20)+sin(155)sin(20) ?
The value of cos(155)cos(20)+sin(155)sin(20) is -(sqrt(2))/2