# Checking your answers in FP3 and FP2

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General guidelines for quick checks on answers

• Where you can, substitute your answer back into the question. If it’s an indefinite integral, differentiate it and see if you get the formula in the question. If it’s an inverted matrix, multiply it by the original matrix and see if you get the identity. If you have to find the equation of a plane passing through points, substitute those points into the equation you’ve got and see if they all satisfy it…
• If the answer is a general formula derived from another general formula in the question, then put the variable or variables equal to easy-to-deal-with values, 0 or 1, and see if your answer looks right
• Draw a rough diagram, or use the diagram given in the question paper.
• Look for clues in the question as to what the examiners expect the answer to be (as in Q.7 in the “specimen” paper)
• Check sum of eigenvalues = trace of matrix
• Use a powerful calculator to check your definite integrals and your matrix inversions