Double angle: tan 2A

Use the double-angle formula to rewrite tan 2A in terms of A.

This formula is given in the exam. It appears on the printed formula list (Senarai Rumus) supplied with every SPM Additional Mathematics paper, so you do not need to memorise it.

What you do need, and what actually earns the marks, is knowing exactly when it applies and how to substitute into it correctly under time pressure. Students often lose marks not because they cannot recall the formula, but because they reach for the wrong one, or substitute the wrong values.

So practise recognising the situation that calls for this formula, not just reciting it.

The reliable habit with any formula is the same: write the formula first, then substitute, then simplify, each on its own line. That single discipline earns method marks even when the arithmetic slips, because SPM marking is analytic and a marker can see the correct approach.

Before substituting, check you have matched each symbol to the right quantity in the question, and mind the details that quietly cost marks, a sign, a unit, an angle mode on the calculator, a condition on the values. When your answer is out, resist re-reading the whole solution; instead check the substitution line first, which is where most errors actually live.

A formula only becomes useful once you have used it inside real questions, so the best practice is not to drill the formula in isolation but to meet it where the exam puts it, as one step inside a longer problem. Work a handful of questions of rising difficulty that call for Double angle: tan 2A, and each time, write the formula, substitute, and simplify as separate lines so the method is visible.

Mark your own work honestly and note any recurring slip. If you find you can state Double angle: tan 2A but freeze when a question does not announce that it is needed, that is the real skill to build, recognising the situation, and it is exactly what a one-to-one teacher can rehearse with you using questions tuned to where you are.