Given any expression of the form \(a\cos x + b\sin x\) it is better to rewrite it into one of the forms \(k\cos (x \pm \alpha )\) or \(k\sin (x \pm \alpha )\) before answering the question.

Can I get free shipping at COS? Yes, COS offers free delivery on orders over £100. If your order is less than this, standard home delivery will cost £4. Your items should be delivered within 4-5 ...

Calculate the length BC. Give the answer to three significant figures. Use the form \(a^2 = b^2 + c^2 - 2bc \cos{A}\) to calculate the length. \(\text{BC}^2 = 3^2 + 7^2 - 2 \times 3 \times 7 \cos ...