Straight LineHardBloom L3

Question

Consider the triangle $OAB$ where $O \equiv (0,0),B(3,4)$. If orthocenter of triangle is $H(1,4)$, then coordinates of ' $A$ is :

Options

A.$\left( 0,\frac{15}{4} \right)$
B.$\left( 0,\frac{17}{4} \right)$
C.$\left( 0,\frac{21}{4} \right)$
D.$\left( 0,\frac{19}{4} \right)$

Solution

Sol. [Key Concept: With $O$ the origin and $B$ given, $A$ lies on the $y$-axis and $AH \perp OB$ locates the orthocentre $H$.]

$BH\bot OA \Rightarrow A$ lies on $y$-axis equation of $AH$ is :

$$y - 4 = - \frac{3}{4}(x - 1)$$

Put $x = 0$,

$$\begin{matrix} \Rightarrow & y = 4 + \frac{3}{4} = \frac{19}{4} \\ \Rightarrow & A \equiv \left( 0,\frac{19}{4} \right) \end{matrix}$$

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