Question
In the given figure, $\angle\text{B}<90^\circ$ and segment $\text{AD}\perp\text{BC}$ show that
  1. $b^2 = h^2 + a^2 + x^2 - 2ax$
  2. $b^2 = a^2 + c^2 - 2ax$

Answer

  1. Since $AD$ perpendicular to $BC$ we obtained two right angled triangles, triangle $ADB$ and triangle $ADC.$
We will use Pythagoras theorem in the right angled triangle $ADC$
$AC^2 = AD^2 + DC^2 ....(1)$
Let us substitute $AD = h, AC = b$ and $DC = (a - x)$ in equation $(1)$ we get,
$b^2 = h^2 + (a - x)^2$
$b^2 = h^2 + a^2 - 2ax + x^2$
$b^2 = h^2 + a^2 + x^2 - 2ax .....(2)$
  1. Let us use Pythagoras theorem in the right angled triangle ADB as shown below,
$AB^2 = AD^2 + BD^2 .....(3)$
Let us substitute $AB = c, AD = h$ and $BD = x$ in equation $(3)$ we get,
$c^2 = h^2 + x^2$​​​​​​​^
Let us rewrite the equation $(2)$ as below,
$b^2 = h^2 + x^2 + a^2 - 2ax .....(4)$
Now we will substitute $h^2 + x^2 = c^2 $ in equation $(4)$ we get,
$b^2 = c^2 + a^2 - 2ax$
Therefore, $b^2 = c^2 + a^2 - 2ax.$

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