Question:
The points P(0, 6), Q(−5, 3) and R(3, 1) are the vertices of a triangle, which is
(a) equilateral
(b) isosceles
(c) scalene
(d) right-angled
Solution:
(d) right-angled
Let P(0, 6), Q(−5, 3) and R(3, 1) be the given points. Then,
$P Q=\sqrt{(-5-0)^{2}+(3-6)^{2}}$
$=\sqrt{(-5)^{2}+(-3)^{2}}$
$=\sqrt{25+9}$
$=\sqrt{34}$ units
$Q R=\sqrt{(3+5)^{2}+(1-3)^{2}}$
$=\sqrt{(8)^{2}+(-2)^{2}}$
$=\sqrt{64+4}$
$=\sqrt{68}$
$=2 \sqrt{17}$ units
$P R=\sqrt{(3-0)^{2}+(1-6)^{2}}$
$=\sqrt{(3)^{2}+(-5)^{2}}$
$=\sqrt{9+25}$
$=\sqrt{34}$ units
$P Q^{2}+P R^{2} \Rightarrow\left\{(\sqrt{34})^{2}+(\sqrt{34})^{2}\right\}=68$
$Q R^{2} \Rightarrow(2 \sqrt{17})^{2}=68$
Thus, $P Q^{2}+P R^{2}=Q R^{2}$
Therefore, ∆PQR is right-angled.