# maths

If sinA=1/2 then find cos^3A-3cosA.

1. 👍 0
2. 👎 0
3. 👁 690
1. if sin A = 1/2 then cos A = (sqrt 3)/2
because that is a 30, 60, 90 triangle
(1/8) 3 * 3^1/2- (3/2) * 3^1/2

= -(9/8) * 3^1/2

1. 👍 0
2. 👎 2

## Similar Questions

1. ### Pre-Calculus

If sinA=3/5 when pi/2 < A < pi and cosB=5/13 when 3pi/2 < B < 2pi, find the exact value of the function cos(5pi/6+B).

2. ### Math

If A and B are acute angle such that SinA=8/17 and CosB=3/5.Find 1, Cos(A+B) 2, Sin(A+B) 3, Sin(A-B)

Angle a lies in the second quadrant and sina=7/25. a) Determine an exact value for cos 2a b) Determine an exact value for sin 2a

4. ### math

if cos(B-C)+cos(C-A)+cos(A-B)=-3/2 then prove that cosA+cosB+cosC=O and sinA+sinB+sinC=O after that prove that cos(B-C)=cos(C-A)=cos(A-B)=-1/2

1.)Find dy/dx when y= Ln (sinh 2x) my answer >> 2coth 2x. 2.)Find dy/dx when sinh 3y=cos 2x A.-2 sin 2x B.-2 sin 2x / sinh 3y C.-2/3tan (2x/3y) D.-2sin2x / 3 cosh 3yz...>> my answer. 2).Find the derivative of y=cos(x^2) with

2. ### Maths

Cos^2A/sinA-cosecA+sinA=0 Prove lHS =RHS

3. ### Math

Suppose sinA = 12/13 with 90º≤A≤180º. Suppose also that sinB = -7/25 with -90º≤B≤0º. Find cos(A - B).

4. ### Maths, Divine International Public School

If 15Cot=8, find (1+SinA)(1-SinA)/(1+CosA)(1-CosA)

1. ### Pre-calculus (Trigonometry)

The rotating spotlight from the Coast Guard ship can illuminate up to a distance of 250 m. An observer on the shore is 500 m from the ship. HIs line of sight to the ship makes an angle of 20 degrees with the shoreline. What length

2. ### Studying for Pre Cal exam

Find the fourth roots of − 1/2 + (square root)3/2 i Write the roots in trigonometric form. A - w 1=cos(35°)+isin(35°) w2 =cos(125°)+isin(125°) w3 =cos(215°)+isin(215°) w4 =cos(305°)+isin(305°) B - w1

3. ### further mathematics

Let P=(cosA sinA) (sinA cosA) Q=(cosB sinA) (sinB cosA) show that PQ=(cosA(A-B) sin(A B)) (sinA(A B) cos(A-B))

4. ### Trigonometry

If sinA=3/5 and cosB=5/13 and if A and B are measures of two angles in Quadrant I, find the exact value of the following functions. cotB = sin2A= 3)cos(5pi/6 + B) = tan(A - pi/4) =