Posted by **sai vishnu** on Thursday, May 2, 2013 at 1:03am.

If cos25+sin25=k then the value os cos20 is ?

- math -
**Steve**, Thursday, May 2, 2013 at 3:08pm
cos20 = cos(70-50) = cos70cos50 + sin70sin50

cos25+sin25 = √2 sin70 = k, so

sin70 = k/√2

cos70 = √(2-k^2) / √2

cos^2 25 + 2sin25cos25 + sin^2 25 = k^2

1 + sin50 = k^2

sin50 = k^2-1

cos50 = k√(2-k^2)

so, now we have

cos 20 = k√(2-k^2)√(2-k^2) / √2 + k(k^2-1)/√2

= (k(2-k^2) + k(k^2-1))/√2

= k/√2

## Answer this Question

## Related Questions

- AP PHYSICS - A golf ball is hit with an initial velocity of 50m/s at an angle of...
- Trig - I don't know the physics behind Snell's Law, but I can do the math Snell'...
- AP Physics - (1.33)sin25.0=(1.50)sinO
- Trig - sin45cos25 + cos45sin25 = ?? a. cos70 b. sin70 c. cos20 d. sin 20 which ...
- math - Evaluate the following with thought the use of a calculator: Sin70.sin25...
- Algebra2 - Help How do I figure out: (cos 40)(cos20) - (sin 40)(Sin 20) Thank ...
- Physics/Math - An iceboat is at rest on a frictionless frozen lake when a sudden...
- Physics - A shopper in a supermarket pushes a cart with a force of 35 N directed...
- Pre-Calculus - I need help on these problems they are from my study guide and i ...
- Physics (Checking answe) - Sorry for re-posting but I need to know if I did it ...