Question

Find a • b. a = 4i + 8j, b = -2i + 3j

Answer 1

U set them equal to each other like,
a=b
4i + 8j = -2i + 3j
+2i +2i
u cancel the ones that equal to 0.
4i + 2i + 8j = 3j
-8j. -8j
4i + 2i = 3j - 8j
6i = -5j answer

Answer 2

$\bf \begin{cases} a=4i+8j\\ b=-2i+3j \end{cases}\implies \begin{cases} a=\ \textless \ 4,8\ \textgreater \ \\ b=\ \textless \ -2,3\ \textgreater \ \end{cases}\\\\ -------------------------------\\\\ \textit{dot product for }\ \textless \ a,b\ \textgreater \ \cdot \ \textless \ c,d\ \textgreater \ \implies (a\cdot c)+(b\cdot d)\\\\ -------------------------------\\\\ a\cdot b\implies (4\cdot -2)+(8\cdot 3)\implies -8+24\implies \boxed{16}$