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ICSE Class X Math 2013 Paper

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Question : 34 of 46
Marks: +1, -0
Without solving the following quadratic equation, find the value of ' pp ' for which the given equation has real and equal roots:
x2+(p3)x+p=0x^2+(p-3) x+p=0
Solution:  
Given: x2+(p3)x+p=0x^2+(p-3) x+p=0
\because Roots are real and equal, then
b24ac=0b^2-4 a c=0
Here we compare the coefficients of a,ba, b and cc with the equation ax2+bx+c=0a x^2+b x+c=0 .
a=1, b=p3  and  c=pa=1,\ b=p-3\;\text{and}\;c=p
Now putting the values of a,ba, b and cc in given equation
(p3)24×1×p=0(p-3)^2-4\times 1\times p=0
p2+96p4p=0p^2+9-6 p-4 p=0
p2+910p=0p^2+9-10 p=0
p210p+9=0p^2-10 p+9=0
p29pp+9=0p^2-9 p-p+9=0
p(p9)1(p9)=0p(p-9)-1(p-9)=0
    (p9)(p1)=0\Rightarrow\;\; (p-9)(p-1)=0
Hence, p=9p=9 or 1
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