Answer:
Two straight lines with slopes m and m' are parallel when m = m'
Two straight lines with slopes m and m' are perpendicular when m × m' = - 1.
Step-by-step explanation:
Let us assume that the two non-vertical lines in the slope-intercept form are
y = mx + c ........... (1) and
y = m'x + c' ............ (2)
If those two lines are parallel then we can say the slope of them will be the same i.e. m = m'
Now, if given two straight lines (1) and (2) are perpendicular to each other and neither of them is parallel to the axes, then we can write m × m' = - 1. (Answer)
3 times (2) gives 3x +9y = -21 (3)
<span>(3) - (1) gives 13y = -39 </span>
<span>y = -3 </span>
<span>Sub. y=-3 into (2) </span>
<span>x + -9 = -7 </span>
<span>x = 2
</span>
<span>Answer = (2,-3) </span>
The answer is 8
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