7. Given non-zero vectors $a , b$ satisfying $| a | = 2 | b |$ and $( a - b ) \perp b$, the angle between $a$ and $b$ is A. $\frac { \pi } { 6 }$ B. $\frac { \pi } { 3 }$ C. $\frac { 2 \pi } { 3 }$ D. $\frac { 5 \pi } { 6 }$
Given non-zero vectors $\boldsymbol { a } , \boldsymbol { b }$ satisfying $| \boldsymbol { a } | = 2 | \boldsymbol { b } |$, and $( \boldsymbol { a } - \boldsymbol { b } ) \perp$
7. Given non-zero vectors $a , b$ satisfying $| a | = 2 | b |$ and $( a - b ) \perp b$, the angle between $a$ and $b$ is\\
A. $\frac { \pi } { 6 }$\\
B. $\frac { \pi } { 3 }$\\
C. $\frac { 2 \pi } { 3 }$\\
D. $\frac { 5 \pi } { 6 }$