Question Details

The vertices of a triangle ABC are A(1, 2), B(–3, 4), C(5, 8), then orthocentre of △ABC is

Options

A

(2/3, 1)

B

( -7/3, 2)

C

(2, 3)

D

(3/2, 1)

Correct Answer :

(3/2, 1)

Solution :

The correct option is (3/2, 1).

Step-by-step Explanation:
The orthocentre of a triangle is the point of intersection of its altitudes. As shown in the provided diagram, we have a triangle ABC with vertices:
A(1, 2)
B(-3, 4)
C(5, 8)
We will find the equations of two altitudes, AD (altitude from vertex A to side BC) and BE (altitude from vertex B to side AC), and solve them to find their intersection point, which is the orthocentre H.

Step 1: Find the equation of altitude AD
First, find the slope of side BC using the slope formula:

mBC = y2 - y1 x2 - x1 = 8 - 4 5 - ( - 3 ) = 4 8 = 1 2

Since the altitude AD is perpendicular to BC, its slope (mAD) is the negative reciprocal of mBC:

mAD = - 1 mBC = - 2

Using the point-slope form, the equation of the line representing altitude AD passing through A(1, 2) is:

y - 2 = - 2 ( x - 1 )

Simplifying this equation:
y-2=-2x+2
2x+y=4    — (Equation 1)

Step 2: Find the equation of altitude BE
Next, find the slope of side AC:

mAC = 8 - 2 5 - 1 = 6 4 = 3 2

Since the altitude BE is perpendicular to AC, its slope (mBE) is the negative reciprocal of mAC:

mBE = - 1 mAC = - 2 3

Using the point-slope form, the equation of the line representing altitude BE passing through B(-3, 4) is:

y - 4 = - 2 3 ( x + 3 )

Simplifying this equation:
3(y-4)=-2(x+3)
3y-12=-2x-6
2x+3y=6    — (Equation 2)

Step 3: Solve the linear equations to find the orthocentre
We have the following system of linear equations:
1) 2x+y=4
2) 2x+3y=6
Subtract Equation 1 from Equation 2:

( 2 x + 3 y ) - ( 2 x + y ) = 6 - 4
2 y = 2
y = 1

Substitute y=1 back into Equation 1:
2x+1=4
2x=3

x = 3 2

Thus, the intersection point of the altitudes is the orthocentre H321.

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