ICSE Class X Math 2014 Solved Paper

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Question : 8
Total: 52
Calculate the ratio in which the line joining A(−4,2) and B(3,6) is divided by point P(x , 3). Also find (i) x (ii) Length of AP .
Solution:  
Let P(x,3) divide the line segment joining the points A(−4,2) and B(3,6) in the ratio k:1

∴ Coordinates of P is
(‌
m1x2+m2x1
m1+m2
,‌
m1y2+m2y1
m1+m2
)
=(‌
3k−4
k+1
,‌
6k+2
k+1
)

But coordinate of P is (x,3)
⇒‌‌‌
6k+2
k+1
‌
=3

6k+2‌=3k+3
3k‌=1⇒k=‌
1
3

∴ The required ratio is ‌
1
3
:1
i.e., 1:3 (internally)
(i) Now x=‌
3k−4
k+1

Putting k=‌
1
3
, we get
x‌=‌
3×
1
3
−4
1
3
+1

‌=‌
1−4
1+3
3
=‌
−3
4∕3
=‌
−9
4


(ii) ∴ Coordinate of P is (‌
−9
4
,3
)

‌ Length of AP ‌‌=√(x2−x1)2+(y2−y1)2
‌=√(−‌
9
4
+4
)
2
+(3−2)2
.

‌=√(‌
−9+16
4
)
2
+(1)2

‌=√‌
49
16
+1
=√‌
49+16
16

‌=√‌
65
16
=‌
√65
4
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