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(i) The line 4x - 3y + 12 = 0 meets the x-axis at A. Write down the coordinates of A.

(ii) Determine the equation of the line passing through A and perpendicular to 4x - 3y + 12 = 0.

Straight Line Eq

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Answer

(i) When the line meets x-axis, its y-coordinate = 0.

So, putting y = 0 in 4x - 3y + 12 = 0, we get

⇒ 4x - 3(0) + 12 = 0
⇒ 4x = -12
⇒ x = -3.

Hence, the line meets the x-axis at A(-3, 0).

(ii) Converting 4x - 3y + 12 = 0, in the form y = mx + c.

⇒ 4x - 3y + 12 = 0

⇒ 3y = 4x + 12

⇒ y = 43x+4\dfrac{4}{3}x + 4

Comparing the above equation with y = mx + c we get,

Slope (m1) = 43\dfrac{4}{3}

Let the slope of the line perpendicular to the given line be m2.

∴ m1 × m2 = -1

43×m2=1m2=34.\Rightarrow \dfrac{4}{3} \times m2 = -1 \\[1em] \Rightarrow m2 = -\dfrac{3}{4}.

Equation of the line having slope = 34-\dfrac{3}{4} and passing through (-3, 0) can be given by,

yy1=m(xx1)y0=34(x(3))4y=3(x+3)4y=3x94y+3x+9=0.\Rightarrow y - y1 = m(x - x1) \\[1em] \Rightarrow y - 0 = -\dfrac{3}{4}(x - (-3)) \\[1em] \Rightarrow 4y = -3(x + 3) \\[1em] \Rightarrow 4y = -3x - 9 \\[1em] \Rightarrow 4y + 3x + 9 = 0.

Hence, the equation of the line is 3x + 4y + 9 = 0.

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