Math

Can someone please check my answers!
2. Find value of cos(255degrees)cos(105degrees)
root3 - 2 / 4

3. cos(pi/12) - cos(5pi/12)
Is it root3/4?

4. Use the appropriate sum-to-product formula to rewrite the expression sin6x - sin9x
I don't really understand how to do these, but I got -2sin(3x/2)cos(15x/2)..

5. same type of question: rewrite the expression cos4x - cos3x
Is it cosx??

  1. 👍 0
  2. 👎 0
  3. 👁 178
  1. on all these, they are the same thing. I am not certain how you see 4,5 as different.

    look here: http://www.sosmath.com/trig/Trig5/trig5/trig5.html Print that out. Notice the sum to product formulas. If you were my student, I would have you write each formula on a flash card until you memorized it.

    work on using those formulas on that page.

  2. Okay, I understand 4 and 5. But what about 2 and 3?

    1. 👍 0
    2. 👎 0
  3. Nevermind, I get it

    1. 👍 0
    2. 👎 0
  4. check my solutions for #1, and #2
    http://www.jiskha.com/display.cgi?id=1370293791

    1. 👍 0
    2. 👎 0
    posted by Reiny
  5. 3. CosA-cosB= -2(sin((a+b)/2)*sin((a-b)/2)
    THEN
    COS(pi/12) - cos(5pi/12)
    = -2(sin( SUM/2)*sin(DIFF/2)
    = -2(SIN 6pi/24 *SIN(-4pi/24))
    = -2 SIN pi/4 * SIN -pi/6)
    = 2SIN (45)* SIN30
    = SQRT2*1/2=.707

    2/ USE THE FORMULA

    COSa*COSb= 1/2 (COS(A-B)+COS(a+B) )

Respond to this Question

First Name

Your Response

Similar Questions

  1. Math

    1. use the suitable product-to-sum formula to rewrite the following expression: sin(13x/2)sin(5x/2) 2. Find value of cos(255degrees)cos(105degrees) is it 1/4? 3. cos(pi/12) - cos(5pi/12) root3/4? 4. Use the appropriate

    asked by mysterychicken on June 3, 2013
  2. calculus

    pleaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaasw help can you pleaaaaase help me find the area between y=cos(4x) and y=1-cos(4x) 0

    asked by aymal on May 2, 2010
  3. Precalculus

    Solve Cos^2(x)+cos(x)=cos(2x). Give exact answers within the interval [0,2π) Ive got the equation down to -cos^2(x)+cos(x)+1=0 or and it can be simplified too sin^2(x)+cos(x)=0 If you could tell me where to go from either of

    asked by Josh on February 23, 2012
  4. Math - Solving Trig Equations

    What am I doing wrong? Equation: sin2x = 2cos2x Answers: 90 and 270 .... My Work: 2sin(x)cos(x) = 2cos(2x) sin(x) cos(x) = cos(2x) sin(x) cos(x) = 2cos^2(x) - 1 cos(x) (+/-)\sqrt{1 - cos^2(x)} = 2cos^2(x) - 1 cos^2(x)(1 -

    asked by Anonymous on November 24, 2007
  5. maths

    Find the roots of z^6 + 1 and hence resolve z^6 + 1into read quadratic factors; deduce that cos3x = 4[cos(x) -cos(pi/6)][(cos(x) -cos(pi/2)][(cos(x) -cos(5pi/6)]

    asked by jake on November 10, 2008
  6. maths

    Find the roots of z^6 + 1 and hence resolve z^6 + 1into read quadratic factors; deduce that cos3x = 4[cos(x) -cos(pi/6)][(cos(x) -cos(pi/2)][(cos(x) -cos(5pi/6)]

    asked by jake on November 10, 2008
  7. Trigonometry (repost Reiny)

    at 1:35am I posted ; Write equivalent equations in the form of inverse functions for a.)x=y+cos theta b.)cosy=x^2 my answers were a.) x= y+ cos theta cos theta = x-y theta = cos^-1(x-y) b.) cosy=x^2 cos(y) = x^2 y = Cos^-1(x^2)

    asked by anon on March 3, 2011
  8. math

    Find the exact value of cos 300 degrees. thanks guys cos 300 = 1/2 = 0.500 how do you know? I am supposed to show my work. You ought to know the rule on 30-60-90 triangles. If the hyp is 2, the shorter side is 1, and the longer

    asked by Bill on June 2, 2007
  9. Trigonometry(please Clarify)

    I posted before ; Write equivalent equations in the form of inverse functions for a.)x=y+cos theta b.)cosy=x^2 my answers were a.) x= y+ cos theta cos theta = x-y theta = cos^-1(x-y) b.) cosy=x^2 cos(y) = x^2 y = Cos^-1(x^2) your

    asked by anon on March 4, 2011
  10. TRIG!

    Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6 x=1 - (3/4)sin^2 2x work on one side only! Responses Trig please help! - Reiny, Monday, February 23, 2009 at 4:27pm LS looks like the sum of cubes sin^6 x +

    asked by hayden on February 23, 2009

More Similar Questions