又係功課..今次係計.
為表我有try過...唔係想問完人抄..
我打我點做...
2sinxcosx-3^(1/2)cosx=0
4sin^2(x)cos^2(x) =9cos^2(x)
4cos^2(x)-4cos^4 (x) =9cos^2(x)
4cos^4(x)+5cos^2(x) =0
cos^2(x)=0 or 4cos^2(x) +5=0
cos^2(x) =-5/4 (rej.)
第2題
cos^2(x)-sin^2 (x)=sin^4(x)+cos^4(x)
cos^2+1-sin^2(x) =1-2sin^2(x)cos^2(x)
2cos^2(x) =-2sin^2(x)cos^2(x)
1 = -sin^2(x)
sin ^2(x) = -1 (rej.)
但係個答案同書比個一個一d都唔同