Challenging +1.2 This is a structured FP3 differential equations question with clear scaffolding through parts (a) and (b). While it involves second-order DEs and substitution (Further Maths content), the question guides students through each step: deriving the chain rule results, verifying the transformation, then solving a standard constant-coefficient DE before back-substituting. The algebraic manipulation requires care but follows predictable patterns. Slightly above average difficulty due to the multi-step nature and Further Maths content, but the scaffolding and standard techniques keep it accessible.
Given that \(x = t ^ { \frac { 1 } { 2 } } , x > 0 , t > 0\) and \(y\) is a function of \(x\), show that:
\(\frac { \mathrm { d } y } { \mathrm {~d} x } = 2 t ^ { \frac { 1 } { 2 } } \frac { \mathrm {~d} y } { \mathrm {~d} t }\);
(2 marks)
\(\frac { \mathrm { d } ^ { 2 } y } { \mathrm {~d} x ^ { 2 } } = 4 t \frac { \mathrm {~d} ^ { 2 } y } { \mathrm {~d} t ^ { 2 } } + 2 \frac { \mathrm {~d} y } { \mathrm {~d} t }\).
(3 marks)
Hence show that the substitution \(x = t ^ { \frac { 1 } { 2 } }\) transforms the differential equation
$$x \frac { \mathrm {~d} ^ { 2 } y } { \mathrm {~d} x ^ { 2 } } - \left( 8 x ^ { 2 } + 1 \right) \frac { \mathrm { d } y } { \mathrm {~d} x } + 12 x ^ { 3 } y = 12 x ^ { 5 }$$
into
$$\frac { \mathrm { d } ^ { 2 } y } { \mathrm {~d} t ^ { 2 } } - 4 \frac { \mathrm {~d} y } { \mathrm {~d} t } + 3 y = 3 t$$
(2 marks)
Hence find the general solution of the differential equation
$$x \frac { \mathrm {~d} ^ { 2 } y } { \mathrm {~d} x ^ { 2 } } - \left( 8 x ^ { 2 } + 1 \right) \frac { \mathrm { d } y } { \mathrm {~d} x } + 12 x ^ { 3 } y = 12 x ^ { 5 }$$
giving your answer in the form \(y = \mathrm { f } ( x )\).