Question

Find a • b. a = 5i + 7j, b = -4i + 3j

Answer 1

Answer:

$a \cdot b = 1$

Step-by-step explanation:

$a = 5i + 7j$

$b = -4i + 3j$

$a = a_xi + a_yj$

$b = b_xi + b_yj$

$a \cdot b = a_xb_x + a_yb_y$

$a \cdot b = (5)(-4) + (7)(3)$

$a \cdot b = -20 + 21$

$a \cdot b = 1$

Answer 2

Answer:

$\boxed{-20i^2 -13ij+21j^2}$

Step-by-step explanation:

$\sf Plug \ in \ the \ values.$

$(5i+7j) \cdot (-4i+3j)$

$\sf Expand \ brackets.$

$5i(-4i+3j)+7j(-4i+3j)$

$-20i^2 +15ij+-28ij +21j^2$

$\sf Combine \ like \ terms.$

$-20i^2 -13ij+21j^2$