0606 P22 - Nov 2018 - Q5 - 5 marks
8529
Solve the simultaneous equations
\(\frac{8^{p+1}}{4^q}=2^{11}, \qquad \frac{3^{2p+5}}{27^{1/3}}=9^{3q}.\)
Solution
Answer: \(p=4\), \(q=2\).
Write all terms in the first equation as powers of \(2\):
\(8^{p+1}=2^{3(p+1)}, \qquad 4^q=2^{2q}.\)
So
\(\frac{2^{3(p+1)}}{2^{2q}}=2^{11}.\)
Equating powers gives
\(3p+3-2q=11.\)
Thus
\(3p-2q=8. \tag{1}\)
For the second equation, write everything as powers of \(3\):
\(27^{1/3}=3, \qquad 9^{3q}=3^{6q}.\)
So
\(\frac{3^{2p+5}}{3}=3^{6q}.\)
Equating powers gives
\(2p+5-1=6q,\)
so
\(2p-6q=-4. \tag{2}\)
Solving (1) and (2), from (2)
\(p=3q-2.\)
Substitute into (1):
\(3(3q-2)-2q=8.\)
Hence
\(7q=14, \qquad q=2.\)
Then
\(p=3(2)-2=4.\)
Therefore
\(\boxed{p=4,\quad q=2}.\)