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The equation of line of intersection of the planes x+y+3z=7x + y + 3z = 7 and x−y+2z=3x - y + 2z = 3 is:

Solution

✅ Correct Option: 4

Direction of line =n1×n2= n_1 \times n_2 where n1=(1,1,3)n_1 = (1,1,3) and n2=(1,−1,2)n_2 = (1,-1,2).

n1×n2=(1⋅2−3⋅(−1), 3⋅1−1⋅2, 1⋅(−1)−1⋅1)=(5,1,−2)n_1 \times n_2 = (1\cdot 2 - 3\cdot(-1),\ 3\cdot 1 - 1\cdot 2,\ 1\cdot(-1) - 1\cdot 1) = (5, 1, -2).

For a point: set z=0z = 0: x+y=7, x−y=3⇒x=5,y=2x + y = 7,\ x - y = 3 \Rightarrow x = 5, y = 2.

Line: x−55=y−21=z−2\frac{x-5}{5} = \frac{y-2}{1} = \frac{z}{-2}.

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