Lesson Example Discussion Quiz: Class Homework |
Step-4 |
Title: Orthocentre |
Grade: 7-a Lesson: S3-L7 |
Explanation: |
Step | Type | Explanation | Answer |
---|---|---|---|
1 |
Problem |
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2 |
Given |
Vertices of triangle are \$(-1, 3), (2, -1)\$ and \$(0, 0)\$. |
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3 |
Assume |
Let \$A(-1, 3), B(2, -1)\$ and \$C(0, 0)\$. Let AD and BE be the altitudes. |
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4 |
Step |
Slope of line joining points \$B(2, -1)\$ and \$C(0, 0)\$ is |
\begin{align} \require{cancel} \text{Slpoe of BC } &= \frac{0 + 1}{0 - 2} \\ &= \frac{-1}{2} \\ &= - \frac{1}{2} \\ \end{align} |
5 |
Step |
Since AD is perpendicular to BC. The slope of the altitude AD = \$ 2\$. Equation of altitude AD is |
\begin{align} \require{cancel} && y - 3 &= 2(x + 1) \\ \Rightarrow && y - 3 &= 2x + 4 \\ \Rightarrow && 2x - y &= -5 \tag{1}\\ \end{align} |
6 |
Step |
Slope of line joining points \$(-1, 3)\$ and \$(0, 0)\$. |
\begin{align} \require{cancel} \text{Slpoe of AC } &= \frac{0 - 3}{0 + 1} \\ &= \frac{-3}{1} \\ &= -3 \\ \end{align} |
7 |
Step |
BE is perpendicular to AC. The slope of the altitude BE \$= \frac{1}{3} \$. Equation of BE is |
\begin{align} \require{cancel} y + 1 &= \frac{1}{3}(x – 2) \\ 3y – 3 &= x - 2 \\ x - 3y &= 5 \tag{2} \\ \end{align} |
8 |
Step |
Solving equation (1) and (2) \$2x - y = -5 \$ and \$x - 3y = 5 \$, |
(1) \$\times\$ 1 \begin{align} 2x – y = -5& \\ \underline{+ 2x – 6y = 10}& \\ 5y = - 15& \\ \\ y = -\frac{15}{5} \\ y = - 3 \\ \end{align} |
9 |
Step |
Substitute \$y = -3\$ in (1). |
\begin{align} \require{cancel} 2x - (-3) &= -5 \\ 2x + 3 &= -5 \\ 2x &= - 8 \\ x &= - 4 \end{align} |
10 |
Step |
Answer |
The orthocentre is \$(-4, -3)\$. |
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