Circles
Grade 11

Question:

<p>Let <span class="math-tex">\(A B C\)</span> be the triangle such that the equations of lines <span class="math-tex">\(A B\)</span> and <span class="math-tex">\(A C\)</span> be <span class="math-tex">\(3 y-x=2\)</span> and <span class="math-tex">\(x+y=2\)</span>, respectively, and the points <span class="math-tex">\(B\)</span> and <span class="math-tex">\(C\)</span> lie on <span class="math-tex">\(x\)</span>-axis. If <span class="math-tex">\(P\)</span> is the orthocentre of the triangle <span class="math-tex">\(A B C\)</span>, then the area of the triangle <span class="math-tex">\(P B C\)</span> is equal to</p>
<p style="display:inline">4</p>
<p style="display:inline">6</p>
<p style="display:inline">8</p>
<p style="display:inline">10</p>

Step-by-Step Solution

Key Concept: Determine the coordinates of B, C, and orthocenter P using properties of altitudes and line intersections, then use the x-axis segment BC as the triangle's base.
<p><img src="https://media-mycbseguide.s3.amazonaws.com/images/question_images/1775818375-hdqdn4.jpg" style="height:149px; width:200px" /><br /> <span class="math-tex">$x=1$</span><br /> We are given triangle <span class="math-tex">$A B C$</span> with:</p> <ul style="list-style-type:disc"> <li>Line AB : <span class="math-tex">$3 y-x=2$</span></li> <li>Line AC: <span class="math-tex">$x+y=2$</span></li> <li>Points B and C lie on the x-axis.</li> <li><span class="math-tex">$P$</span> is the orthocenter of triangle <span class="math-tex">$A B C$</span>.</li> </ul> <p>The point A is the intersection of lines AB and AC, A(1, 1)<br /> The orthocentre is the intersection point of the altitudes of the triangle.<br /> <strong>Altitude from A to BC:</strong></p> <ul style="list-style-type:disc"> <li>Since BC lies on the <span class="math-tex">$x$</span>-axis, the altitude from A is a vertical line passing through A.</li> <li>Equation: <span class="math-tex">$x=1$</span></li> </ul> <p><strong>Altitude from B to AC:</strong></p> <ul style="list-style-type:disc"> <li>Slope of AC: From <span class="math-tex">$x+y=2$</span>, slope <span class="math-tex">$m_{{AC}}=-1$</span></li> <li>Slope of altitude BP: Perpendicular to <span class="math-tex">${AC}, {so}\ m_{{BP}}=1$</span>.</li> <li>Equation of BP: <span class="math-tex">$y+0=1(x+2)$</span> or <span class="math-tex">$y=x+2$</span>.</li> </ul> <p>Find <span class="math-tex">${P}$</span>:</p> <ul style="list-style-type:disc"> <li>Intersection of <span class="math-tex">$x=1$</span> and <span class="math-tex">$y=x+2$</span> :<br /> <span class="math-tex">$y=1+2=3$</span></li> <li>Thus, <span class="math-tex">${P}(1,3)$</span>.</li> </ul> <p>Using the area formula for a triangle:</p> <p>Area <span class="math-tex">$=\frac{1}{2} \times$</span> base &times; height</p> <p><span class="math-tex">$=\frac{1}{2} \times 4 \times 3=6$</span></p>
Correct Answer: B

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