Jacob has to solve the equation
3−sinx=1+2cos2x 3 - \sin x = 1 + 2\cos^2 x 3−sinx=1+2cos2xwhere −180∘≤x<180∘-180^{\circ} \leq x < 180^{\circ}−180∘≤x<180∘
Jacob's working is as follows:
3−sinx=1+2cos2x2−sinx=2cos2x2−sinx=2(1−sin2x)2−sinx=2−2sin2x−sinx=−2sin2x1=2sinxsinx=0.5x=30∘ \begin{aligned} 3 - \sin x &= 1 + 2\cos^2 x \\ 2 - \sin x &= 2\cos^2 x \\ 2 - \sin x &= 2(1 - \sin^2 x) \\ 2 - \sin x &= 2 - 2\sin^2 x \\ -\sin x &= -2\sin^2 x \\ 1 &= 2\sin x \\ \sin x &= 0.5 \\ x &= 30^{\circ} \end{aligned} 3−sinx2−sinx2−sinx2−sinx−sinx1sinxx=1+2cos2x=2cos2x=2(1−sin2x)=2−2sin2x=−2sin2x=2sinx=0.5=30∘Explain the two errors that Jacob has made.
Write down all the values of x x\,x that satisfy the equation
3−sinx=1+2cos2x 3 - \sin x = 1 + 2\cos^2 x 3−sinx=1+2cos2xwhere −180∘≤x<180∘-180^{\circ} \leq x < 180^{\circ}−180∘≤x<180∘
Practise Edexcel AS Level Maths Trigonometric Identities and Equations with exam-style questions for AS Level Maths. 30 questions covering 10.1 Angles in all four Quadrants, 10.2 Exact Values of Trigonometric Ratios, 10.3 Trigonometric Identities, 10.4 Solving Trigonometric Equations, 10.5 Harder Trigonometric Equations, and 10.6 Equations and Identities, matched to the Edexcel AS Level Maths (8MA0) specification and written in Paper 1 and Paper 2 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.