Trigo!

posted by .

Ok, i did this maths trigo question, that says sinx-cos=2/3. I squared it on both sides to get sin2x=5/9 and did the sum. In the end i got two solutions, 16.9 and 73.1. However, when i substituted the answers back into the equation, only one of the 2 answers was correct! The other one didn't work out! Why is this so? I'm pretty sure both answers are correct, so what's going on? Please help!

  • Trigo! -

    You have done the right step, check your answers after you have squared each side of an equation.

    Take a simple case of
    x=-4
    square both sides,
    x²=(-4)²=16
    x=√16=±4
    check:
    x=-4 OK
    x=+4 not a solution.

    In your case, the solution of 73.126° is correct. The other one is false.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. calc

    Where do I start to prove this identity: sinx/cosx= 1-cos2x/sin2x please help!! Hint: Fractions are evil. Get rid of them. Well, cos2x = cos 2 x - sin 2 x, so 1-coscx = 1 - cos 2 x - sin 2 x = 1 - cos 2 x + sin 2 x You should be able …
  2. Trig.......

    I need to prove that the following is true. Thanks (2tanx /1-tan^x)+(1/2cos^2x-1)= (cosx+sinx)/(cosx - sinx) and thanks ........... check your typing. I tried 30º, the two sides are not equal, they differ by 1 oh , thank you Mr Reiny …
  3. check math

    Here are my answers. Can you check if I got the right answers?
  4. Math, derivatives

    f(x) = x² + 2Cos²x, find f ' (x) a) 2(x+cos x) b) x - sin x c) 2x + sin x d)2(x - sin2x) I got neither of these answers, since the 2nd part should be chain rule, right?
  5. Trigo help!

    Ok, i've tried this question, and it brings me to no answers. Please help! Prove the following: secY(1+tanY)=6cosecY my workings: LeftHandSide: secY + tanY/cosY = 1/cosY + sinY/cos^2Y =(cosY+sinY)/cos^2Y = ?
  6. maths - trigonometry

    I've asked about this same question before, and someone gave me the way to finish, which I understand to some extent. I need help figuring out what they did in the second step though. How they got to the third step from the second. …
  7. maths trigo

    prove that sin(n+1)A-sin(n-1)A/cos(n+1)A+2cos(nA)+cos(n-1)A=tanA/2
  8. maths

    by equating the coefficients of sin x and cos x , or otherwise, find constants A and B satisfying the identity. A(2sinx + cosx) + B(2cosx - sinx) = sinx + 8cosx I got A = 2, B = 3, which the answers said were correct. However, another …
  9. Math

    Find all solutions to the equation sqrt(2-3x)= 9. Express your answer as a common fraction. I squared both sides and I got 4-9z^2=81 and then -9z^2=77 then I divided both sides by -9 and now I am stuck, I know I can square root both …
  10. Math

    I need help solving for all solutions for this problem: cos 2x+ sin x= 0 I substituted cos 2x for cos^2x-sin^2x So it became cos^2(x)-sin^2(x) +sinx=0 Then i did 1-sin^2(x)-sin^2(x)+sinx=0 = 1-2sin^2(x)+sinx=0 = sinx(-2sinx+1)=-1 What …

More Similar Questions