Is the line 3x + 4y + 7 = 0 perpendicular to the line 28x - 21y + 50 = 0?

Given lines,

⇒ 3x + 4y + 7 = 0 and 28x - 21y + 50 = 0

⇒ 4y = -3x - 7 and 21y = 28x + 50

⇒ y = $-\dfrac{3}{4}x - \dfrac{7}{4}$ and y = $\dfrac{28}{21}x + \dfrac{50}{21}$

Comparing above equations with y = mx + c we get,

Slope of 1st line = $-\dfrac{3}{4}$

Slope of 2nd line = $\dfrac{28}{21} = \dfrac{4}{3}$

Since,

Slope of 1st line × Slope of 2nd line = $-\dfrac{3}{4} \times \dfrac{4}{3} = -1.$

Hence, the lines 3x + 4y + 7 = 0 and 28x - 21y + 50 = 0 are perpendicular to each other.