標題:
超急問 sin(2x+30)=cos(51-x) F2數
發問:
sin(2x+30)=cos(51-x) Step Please 更新: 求X 更新 2: cos(40-3x)=sin(7x+2)
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最佳解答:
sin(2x+30)=sin[90-(51-x)] 0
其他解答:
sin(2x+30)=cos(51-x) cos [90 -(2x+30)]=cos(51-x) [[ trigonometric idenities : cosx = sin(90-x) ]] ------------90-2x-30=51-x [[約左個cos]] ------------90-30-2x=51-x ----------------60-51=2x-x [[ 51調去左面 ||| 2x調去右面]] ------------------------x=9 ___cos(40-3x)=sin(7x+2) sin[90-(40-3x)]=sin (7x+2) [[trigonometric idenities : sinx = cos(90-x) ]] -------90-40+3x=7x+2 [[約左個sin || 因為負負得正..所以-3x變左+3x ]] --------------50-2=7x-3x [[ 調個2去左面..調3x去右面]] -----------------4x=48 ----------------- x=12|||||∵cos a=sin(90-a) ∴sin(2x+30)=cos(51-x) →sin(2x+30)=sin[90-(51-x)] →2x+30=39+x →3x=9 →x=3 ∴cos(40-3x)=sin(7x+2) →sin[90-(40-3x)]=sin(7x+2) →50+3x=7x+2 →50-2=7x-3x →4x=48 →x=12
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