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ICSE Class X Math 2016 Solved Paper

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Question : 20
Total: 57
SECTION - II

Solve the quadratic equation x2−3(x+3)= 0 ; Give your answer correct to two significant figures.
Solution:  
Given : x2−3(x+3)=0
x2−3x−9=0
Comparing x2−3x−9=0 with ax2+bx+c =0, we get
We know,
a=1,b=−3,c=−9
x‌=‌
−b±√b2−4ac
2a
‌=‌
−(−3)±√(−3)2−4×1×(−9)
2×1
‌=‌
3±√9+36
2
=‌
3±√45
2
‌=‌
3±3√5
2
=‌
3±3×2.236
2
x‌=‌
3±6.708
2
x‌=‌
3+6.708
2
‌ and ‌‌
3−6.708
2
x‌=4.85‌, and ‌−1.85
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