# math(Trigonometry)

posted by .

2cos^2 theta + 5 sin theta - 4 = 0

• math(Trigonometry) -

2(1-sin^2) + 5sin - 4 = 0
2sin^2 - 5sin + 2 = 0
(2sin-1)(sin-2) = 0
sin = 1/2 or 2
...

• math(Trigonometry) -

can give me a further and detail explanation where did the theta on the 5 and the formula on changing the cos theta.

• math(Trigonometry) -

you know that cos^2 = 1-sin^2
the rest is just algebra I
I dropped the thetas just for ease of typing.

Naturally, sin can never be 2, so that's a non-solution, even though it does satisfy the original equation.

## Similar Questions

1. ### Trig

Which expression equivalent to: cos(theta + pi/2). A)cos theta B)-cos theta C)sin theta D)-sin theta my book doesnt give examples of this but my crack at it would be C b/c distributive property?
2. ### Calculus

I wanted to confirm that I solved these problems correctly (we had to convert the polar curves to Cartesian equations). 1.rcos(theta)=1 x=1 2.r=2*sin(theta)+2*cos(theta) r^2=2rsin(theta)+2rcos(theta) x^2+y^2=2y+2x (a little unsure …
3. ### trigonometry

can you correct the rest for me please? Express each as a function of theta: a. sin (270deg + theta)= cos theta b. cos (pi + theta)= -cos theta c. tan (810 + theta)= ?
4. ### trigonometry

can you correct the rest for me please? Express each as a function of theta: a. sin (270deg + theta)= cos theta b. cos (pi + theta)= -cos theta c. tan (810 + theta)= ?
5. ### Trigonometry

determine real numbers a and b so that the expression 8sin^2(theta) + 2cos^2(theta) can be rewritten as (a)sin^2(theta) + b?
6. ### math(Trigonometry)

sin 2 theta + cos theta = 0 so, we use sin 2 theta = 2 sin theta cos theta right?
7. ### Trigonometry

I am having problems with proving identities that has a number and an exponent with it. Like: *2cosxcsc2x = cscx *sin^2 2x = 4sin^2 x cos^2 x *cot2(theta)=csc(theta)-2sin(theta)/2cos(theta)
8. ### Precalculus

2cos^2(theta) + Sin(theta)=1 I know I have to use the quadratic formula but i'm having trouble after I convert the Cos^2(theta) to (1-Sin^2(theta))
9. ### Trigonometry

Prove the following identities: 1. (tan theta - sin theta)^2 + (1-cos theta)^2 = (1-sec theta) ^2 2. (1-2cos^2 theta) / sin theta cos theta = tan theta - cot theta 3. (sin theta + cos theta ) ^2 + (sin theta - cos theta ) ^2 = 2 Thank …
10. ### Trigonometry

Prove the following identities: 1. (tan theta - sin theta)^2 + (1-cos theta)^2 = (1-sec theta) ^2 2. (1-2cos^2 theta) / sin theta cos theta = tan theta - cot theta 3. (sin theta + cos theta ) ^2 + (sin theta - cos theta ) ^2 = 2 Thank …

More Similar Questions