NCERT Solutions
Class 11 Maths
Straight Lines

Ex.10.1 Q.6
Without using the Pythagoras theorem, show that the points (4, 4), (3, 5) and (–1, –1) are the vertices of a right-angled triangle.
The vertices of the given triangle are A (4, 4), B (3, 5), and C (–1, –1).
It is known that the slope (m) of a non-vertical line passing through the points (x1, y1) and (x2, y2) is given by
m = (y2 – y1) ÷ (x2 – x1), x2 ≠ x1
Slope of AB (m1) = (5 – 4) ÷ (3 – 4) = -1
Slope of BC (m2) = (-1 – 5) ÷ (-1 – 3) = =
Slope of CA (m3) = (4 + 1) ÷ (4 + 1) = = 1
It is observed that m1 × m3 = –1
This shows that line segments AB and CA are perpendicular to each other i.e., the given triangle is right-angled at A (4, 4).
Thus, the points (4, 4), (3, 5), and (–1, –1) are the vertices of a right-angled triangle.