Let ABC be and equilateral triangle and let AD \\(\\perp\\) BC.<\/p>\n
In \\(\\triangle\\) ADB and ADC, we have :<\/p>\n
AB = AC\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 (given)<\/p>\n
AD = AD\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0(common side of triangle)<\/p>\n
and \\(\\angle\\) ADB = \\(\\angle\\) ADB\u00a0 \u00a0 \u00a0 \u00a0 (each 90)<\/p>\n
By RHS criteria of congruence, we have :<\/p>\n
\\(\\triangle\\)\u00a0 ADB \\(\\cong\\) \\(\\triangle\\) ADC<\/p>\n
So, BD = DC or\u00a0 BD = DC = \\(1\\over 2\\) BC\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0……..(1)<\/p>\n
Since \\(\\triangle\\)\u00a0 ADB is a right triangle, angled at D, by Pythagoras theorem, we have :<\/p>\n
\\({AB}^2\\) = \\({AD}^2\\) + \\({BD}^2\\)<\/p>\n
\\({AB}^2\\) = \\({AD}^2\\) + \\(({1\\over 2}BC)^2\\)\u00a0 \u00a0 \u00a0 \u00a0 (from 1)<\/p>\n
\\({AB}^2\\) = \\({AD}^2\\) + \\({1\\over 4}{BC}^2\\)<\/p>\n
\\({AB}^2\\) = \\({AD}^2\\) + \\({AB}^2\\over 4\\)\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 (\\(\\therefore\\)\u00a0 BC = AB)<\/p>\n
\\({3\\over 4}{AB}^2\\) = \\({AD}^2\\)\u00a0 or\u00a0 \\(3{AB}^2\\) = \\(4{AD}^2\\)<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"
Solution : Let ABC be and equilateral triangle and let AD \\(\\perp\\) BC. In \\(\\triangle\\) ADB and ADC, we have : AB = AC\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 (given) AD = AD\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0(common side of triangle) and \\(\\angle\\) ADB = \\(\\angle\\) ADB\u00a0 \u00a0 \u00a0 \u00a0 (each 90) By RHS criteria of …<\/p>\n