A line has gradient 2/3. What is the gradient of a line perpendicular to it?

A line has gradient $\frac{2}{3}$ . What is the gradient of a line perpendicular to it?

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Determine the equation of the straight line with gradient 1 that passes through $(2; 1)$ .
Determine the equation of the straight line with gradient 1 that passes through $(- 1; - 4)$ .
Determine the equation of the straight line with gradient 3 that passes through $(1; 4)$ .
Determine the midpoint of the line segment joining $A (5; 3)$ and $B (- 1; - 1)$ .
Calculate the distance between $A (3; - 3)$ and $B (11; 3)$ .
Calculate the distance between $A (- 2; 3)$ and $B (4; 11)$ .