# Trigonometry

Write the expression as a trigonometric function of one number.
(cos 20 degrees)(cos 70 degrees)+(sin 20 degrees)(sin 70 degrees)

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1. Have you come across the identity

cos(A-B) = cosAcoB + sinAsinB ?

your question fits that pattern perfectly.

Let me know what you get.

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2. ok I made a mistake in the formula. it's cos(20 degrees)cos(70 degrees)- sin(20 degrees) sin(70 degrees).

so it's a subraction equation not an addition.

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3. and of course there is the matching formula for

cos(A+B) = cosAcosB - sinAsinB

So what do you think?

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4. so it would be cos(20+70)?

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5. cos(20 degrees+70 degrees) i mean

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6. yes, but what is cos(20° + 70°) ??
= cos 90°
= 0

so your
cos(20 degrees)cos(70 degrees)- sin(20 degrees) sin(70 degrees)
= 0

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7. Yeah I got the exact value I just needed it in trigonometric function of one number which would be the degrees of cos.

Thanks!!!

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8. HELP ME !

sin50 cos 20 - cos 50 sin 20
^find exact value

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9. Pls tell me how to find out sin70.Pls

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10. How are the sun 70 degrees and cos 20 seg related

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