Saturday

October 25, 2014

October 25, 2014

Posted by **PDF** on Monday, August 27, 2012 at 2:22am.

1. cos 3t = 4 cosł t-3 cos t

2. sin 4x = 8 sin x cosł x-4 x cos x

(use a double-angle identity)

- trigonometry -
**Reiny**, Monday, August 27, 2012 at 8:01am1.

LS = cos 3t

= cos(2t + t)

= cos2tcost - sin2tsint

= (2cos^2 t - 1)(cost) - 2sintcostsint

= 2cos^3 t - cost - 2sin^2 t cost

= 2cos^3 t - cost - 2(1 - cos^2 t)cost

= 2cos^3 t - cost - 2cost + 2cos^3 t

= 4cos^3 t - 3cost

= RS

for #2, start with

LS = sin(2x + 2x)

= sin2xcos2x + cos2x sin2x

then use the double-angle formulas for each one

simplify very carefully

**Answer this Question**

**Related Questions**

tigonometry - expres the following as sums and differences of sines or cosines ...

Mathematics - Trigonometric Identities - Let y represent theta Prove: 1 + 1/tan^...

trig - Reduce the following to the sine or cosine of one angle: (i) sin145*cos75...

TRIG! - Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6...

algebra - Can someone please help me do this problem? That would be great! ...

Math - Calculus - The identity below is significant because it relates 3 ...

pre-cal - Simplify the given expression........? (2sin2x)(cos6x) sin 2x and cos ...

calculus - Differentiate. y= (cos x)^x u= cos x du= -sin x dx ln y = ln(cos x)^x...

Calc. - Differentiate. y= (cos x)^x u= cos x du= -sin x dx ln y = ln(cos x)^x ln...

Trig! - The identities cos(a-b)=cos(a)cos(b)sin(a)sin(b) and sin(a-b)=sin(a)cos(...