Thursday

December 18, 2014

December 18, 2014

Posted by **Spy[c]** on Wednesday, September 22, 2010 at 10:23pm.

- trig -
**MathMate**, Wednesday, September 22, 2010 at 11:04pmFormulas to remember:

sin(2a)=2sin(a)cos(a)

cos(2a)=cos²(a)-sin²(a)

From the second equation, replace a by a/2 and 2a by a to get

cos(a)=cos²(a/2)-sin²(a/2)

=2cos²(a/2)-1 ...(1)

=1-2sin²(a/2) ...(2)

From (1) we get

cos²(a/2)=(1/2)(1+cos(a))

From (2) we get

sin²(a/2)=(1/2)(1-cos(a))

So

sin(7.5)

=√((1/2)(1-cos(15))

=√((1/2)(1-√((1/2)(1+cos(30))))

=√((1/2)(1-√((1/2)(1+√(3)/2)))

=0.13...

**Answer this Question**

**Related Questions**

tRiG/ AlGeBrA - 1) Use double-angle identities to write the following expression...

trig - 1) Use double-angle identities to write the following expression, using ...

Trig - How do you express sin4x as a trigonometric funcition of x using the ...

trig - Let Q be an acute angle such that sinQ=.6. Find the values of the ...

Trig - find the exact values of the six trig functions of angle... sin(-...

trig - A coil of wire rotating in a magnetic field induces a coltage E=20sin((...

Trigonometry - Identities - If tan 2x = - 24/7, where 90 degrees < x < 180...

math - Can anyone help w/ these. 1) Solve the equation in the internal [0deg, ...

Precalculus - I've tried many times to get the equation to balance using trig ...

Trigonometry - use the appropriate trig identity (sum and difference, half angle...