Help Solving Trig Equation: Cos70°cos20°-sin70°sin20°

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The discussion focuses on solving the trigonometric equation Cos70°cos20° - sin70°sin20°. A participant seeks a formula for cos(a+b), which is expressed as cos a • cos b - sin a • sin b. They struggle to find equivalent angles for 70° and 20°. Another participant points out that cos(20+70) equals cos(90), which simplifies the equation. The conversation highlights the application of trigonometric identities in solving equations.
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Cos70°cos20°-sin70°sin20°

I can't find any of these angles that are equivalent to the basic angles. Thanks
 
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Do you know a formula for cos(a+b) in terms of the trig functions evaluated at a and b?
 
Cost(a+b)=cos a • cos b - sin a • sin b
 
I don't know which angles are equivalent to 70° nor 20°
 
But you know cos(20+70)=cos(90), right?
 
Whoops. Thanks
 

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