Precal/trig

sina=3/5, pi/2<a<pi evaluate cos2a

  1. 👍 0
  2. 👎 0
  3. 👁 68
  1. cos2a = 1 - 2sin^2(a)
    = 1 - 2*9/25
    ...

    in this case, it doesn't really matter which quadrant a is in, as sin^2 is always positive.

    extra credit: which quadrant is 2a in?

    1. 👍 0
    2. 👎 0
    posted by Steve

Respond to this Question

First Name

Your Response

Similar Questions

  1. Trig

    Please help with this one. I've worked it out in so many ways and can't tell what's correct. sinA sinA ----- - ------ 1+sinA 1-sinA Which answer is correct for the problem above? a) 1+cotA b) sinA tanA c) -2tan^2A d) secA cscA

    asked by Jasmine on December 9, 2006
  2. Maths

    Hi, can someone give me the answer to this question: secA-tanA=1/4. Find cosA I got: CosA=4(1-sinA) Is my answer good? Now multply each side by (1+sinA) CosA(1+sinA)=4 cos^2 A CosA=1/4 (1+sinA) 16(1-sinA)=1+sinA 15=17SinA So you

    asked by Shym on June 3, 2007
  3. Math

    Hello I am having trouble with proving this: sinA/secA+secA/cscA = tan(A)(2-sin^2(A)) So far I've gotten SinA/(1/cosA) + (1/cosA)/(1/sinA) SinACosA + sinA/cosA I am stuck here, not even sure if multiplying by the reciprocal was

    asked by Jimbo on April 23, 2019
  4. Math

    In any angle ABC prove that the perimeter = a/Sin A(Sin A + Sin B + Sin C) Start with perimeter = a+b+c but b= aSinB/sinA and c= aSinC/SinA and if you don't remember, a=a=a*SinA/ SinA

    asked by Anonymous on May 27, 2007
  5. 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))

    asked by James on September 17, 2013
  6. Trigonometric Identities

    Verify/prove the following: (sinA+tanA)/(1+secA) = sinA ______________________________ tanu = 1+sinu-cos^2u/cosu(1+sinu) __________________________________ cotu = (2+cscu/secu)-2cosu ______________________________

    asked by Kid on March 14, 2016
  7. Maths

    Prove that [sinA/(1-cosA)-(1-cosA)/sinA]*[cosA/(1+sinA)+(1+sinA)/cosA]=4cosecA I the second part as 2 secA

    asked by Agastya on September 15, 2016
  8. Trig - Ambiguous Cases

    Triangle HAV has

    asked by AlphaPrimes on March 9, 2016
  9. 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

    asked by Lucina on February 27, 2015
  10. trig

    if 5cos A plus 3=0 and 180

    asked by patience morakile on May 13, 2013
  11. Trig

    IfA=340°, prove that 2cosA/2 = -(v1+sinA) - (v1-sinA)

    asked by Kewal on January 12, 2012

More Similar Questions