Hi. I have a problem solving this trigonometrical equation:

6sin(pi+x)+cos(pi/2+x) if cosx=0.6 and 0<x<pi/2

If you can, please ask questions so that I try to answer them myself and solve the equation step by step. I'm not from an English speaking country, but I hope we have similar terms and you understand me.

Do I reduce first? I get -7sinx, but I'm not sure how to use then cosx=0.6, if I reduce -7sinx back to cos I get -7cos(3pi/2+x) here also I don't know how to use cosx=0.6....