A-LevelMathematicsLogarithmic and exponential functions9709/22 · Oct/Nov 2019 · Q25 Marks
Solve the equation |4x + 5| = |x − 7|.
- (i)Solve the equation |4x + 5| = |x − 7|.[3]
- (ii)Hence, using logarithms, solve the equation |2^(y+2) + 5| = |2^y – 7], giving the answer correct to 3 significant figures.[2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.
- [B1] State or imply non-modular equation (4x + 5)² = (x − 7)² or pair of different linear equations
- [M1] Attempt solution of 3-term quadratic equation or pair of linear equations
- [A1] Obtain 2/3 and −4 (SC For x = −4 only, from correct work, allow B1)
- [M1] Apply logarithms and use power law for 2^y = k where k>0 from (i)
- [A1] Obtain -1.32 only (AWRT)
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