f'(x)=(4x³(x+12))'=(4x³)'(x+12)+4x³(x+12)'=12x²(x+12)+4x³×1=12x³+144x²+4x³=16x³+144x²
f''(x)=(16x³+144x²)'=48x²+288x
f''(1/4)=48×(1/4)²+288×(1/4)=48×1/16+288×1/4=3+72=75
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f'(x)=(4x³(x+12))'=(4x³)'(x+12)+4x³(x+12)'=12x²(x+12)+4x³×1=12x³+144x²+4x³=16x³+144x²
f''(x)=(16x³+144x²)'=48x²+288x
f''(1/4)=48×(1/4)²+288×(1/4)=48×1/16+288×1/4=3+72=75