The problem asks us to find the dot product $\vec{a} \cdot \vec{b}$ of two vectors $\vec{a}$ and $\vec{b}$ for two cases: (1) $\vec{a} = (-1, 2)$ and $\vec{b} = (4, 3)$ (2) $\vec{a} = (3, 2)$ and $\vec{b} = (-2, 3)$

GeometryVectorsDot ProductLinear Algebra
2025/5/11

1. Problem Description

The problem asks us to find the dot product ab\vec{a} \cdot \vec{b} of two vectors a\vec{a} and b\vec{b} for two cases:
(1) a=(1,2)\vec{a} = (-1, 2) and b=(4,3)\vec{b} = (4, 3)
(2) a=(3,2)\vec{a} = (3, 2) and b=(2,3)\vec{b} = (-2, 3)

2. Solution Steps

The dot product of two vectors a=(a1,a2)\vec{a} = (a_1, a_2) and b=(b1,b2)\vec{b} = (b_1, b_2) is defined as:
ab=a1b1+a2b2\vec{a} \cdot \vec{b} = a_1b_1 + a_2b_2
(1) Given a=(1,2)\vec{a} = (-1, 2) and b=(4,3)\vec{b} = (4, 3), we have a1=1a_1 = -1, a2=2a_2 = 2, b1=4b_1 = 4, and b2=3b_2 = 3. Thus,
ab=(1)(4)+(2)(3)=4+6=2\vec{a} \cdot \vec{b} = (-1)(4) + (2)(3) = -4 + 6 = 2.
(2) Given a=(3,2)\vec{a} = (3, 2) and b=(2,3)\vec{b} = (-2, 3), we have a1=3a_1 = 3, a2=2a_2 = 2, b1=2b_1 = -2, and b2=3b_2 = 3. Thus,
ab=(3)(2)+(2)(3)=6+6=0\vec{a} \cdot \vec{b} = (3)(-2) + (2)(3) = -6 + 6 = 0.

3. Final Answer

(1) ab=2\vec{a} \cdot \vec{b} = 2
(2) ab=0\vec{a} \cdot \vec{b} = 0

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