Answer:
[tex]\large\boxed{f(a^2)=7a^4-8}[/tex]
Step-by-step explanation:
[tex]f(x)=7x^2-8\\\\f(a^2)\to \text{put}\ x=a^2\ \text{to the equation of the function}\ f:\\\\f(a^2)=7(a^2)^2-8\qquad\text{use}\ (a^n)^m=a^{nm}\\\\f(a^2)=7a^{2\cdot2}-8\\\\f(a^2)=7a^4-8[/tex]
