Wednesday

January 28, 2015

January 28, 2015

Posted by **Sam** on Tuesday, November 5, 2013 at 10:26pm.

Hmm...I don't understand how to proceed. I know I must apply a trig Identity, but which one?

Thanks in advance

- Math - Trigonometry -
**Reiny**, Tuesday, November 5, 2013 at 11:33pmsinØ + cosØ = 1.2

square both sides

sin^2 Ø + 2sinØcosØ + cos^2 Ø = 1.44

but sin^2Ø + cos^2Ø = 1

2sinØcosØ = 0.44

sinØcosØ = .22

now using the fact that

(a+b)^3 = a^3 + 3a^2b + 3ab^2 + b^3

we see that

a^3 + b^3 = (a+b)^3 - 3a^2b - 3ab^2

= (a+b)^3 - 3ab(a+b)

so sin^3 Ø + cos^3 Ø

= (sinØ + cosØ)^3 - 3sinØcosØ (sinØ + cosØ)

= 1.2^3 - 3(.22)(1.2)

=**0.936**

check:

from 2sinØcosØ = .44

sin 2Ø = .44

2Ø = 26.103...

Ø = 13.0519....

then by calculator: sin^3 13.0519° + cos^3 13.0519°

= .93599...

not bad!

- Math - Trigonometry -
**Sam**, Wednesday, November 6, 2013 at 7:15amThanks a lot :)

**Answer this Question**

**Related Questions**

Calculus - I wanted to confirm that I solved these problems correctly (we had to...

trigonometry - can you correct the rest for me please? Express each as a ...

trigonometry - can you correct the rest for me please? Express each as a ...

Trig - Which expression equivalent to: cos(theta + pi/2). A)cos theta B)-cos ...

math(Trigonometry) - sin 2 theta + cos theta = 0 so, we use sin 2 theta = 2 sin ...

Algebra II - Multiple Choice Which expression is NOT equivalent to 1? (theta) ...

Trigonometry - Thank you STEVE!!!!! Suppose that Cos (theta) = 1/square root 2 ...

trig - Hi, I need to find the domain and rnge of the following: 1. X= 1/2 (cos ...

precalc h - sin(theta)/1-cos(theta) + 1-cos(theta)/sin(theta) = 2csc(theta) That...

trigonomtry - can you correct the rest for me please? Express each as a function...