15. The smallest possible value of $\int _ { 0 } ^ { 1 } ( x - a ) ^ { 2 } d x$ as $a$ varies is A $\frac { 1 } { 12 }$ B $\frac { 1 } { 3 }$ C $\frac { 1 } { 2 }$ D $\frac { 7 } { 12 }$ E 2
15. The smallest possible value of $\int _ { 0 } ^ { 1 } ( x - a ) ^ { 2 } d x$ as $a$ varies is
A $\frac { 1 } { 12 }$\\
B $\frac { 1 } { 3 }$\\
C $\frac { 1 } { 2 }$\\
D $\frac { 7 } { 12 }$
E 2\\