Solve the equation \(\displaystyle{\sin{{\left({3}{x}\right)}}}{\cos{{\left({x}\right)}}}={\frac{{23}}{}}\) for \(\displaystyle{x}\in{\left[{0},{\frac{{\pi}}{{{2}}}}\right)}\)

Zack Mora

Zack Mora

Answered question

2022-03-21

Solve the equation sin(3x)cos(x)=23 for x[0,π2) but I could not do it. I tried to develop sin(3x)=sin(x+x+x) and I arrived at the step where the equation becomes (4cos2(x)1)sin(x)cos(x)=23 and I could not go further !

Answer & Explanation

Lana Hamilton

Lana Hamilton

Beginner2022-03-22Added 12 answers

Hint:
2=3sinxcosx(4cos2x1)
Divide both sides by cos4x
3tanx(34tan2x)=2sec4x=2(1+tan2x)2
2t4+12t3+4t29t+2=0
where t=tanx

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