8th Class Mathematics Sample Paper Mathematics Sample Paper - 3

  • question_answer                        Factorise the following :
    (a) \[18+11x+{{x}^{2}}\]
    (b) \[{{y}^{2}}-2y-15\]

    Answer:

    (a)    \[18+\text{11}x+{{x}^{2}}=\text{ }{{x}^{2}}+1\text{1}x+18\]   
    \[={{x}^{2}}+\left( 9+2 \right)\text{ }x+18\]      
    \[={{x}^{2}}+9x+2x+18\]
    \[=x(x+9)+2(x+9)\]
    = (x + 9) (x + 2)  
    (b)  \[{{y}^{2}}-2y-15={{y}^{2}}-(5-3)y-15\]
    \[={{y}^{2}}-5y+3y-15~\] \[=y\left( y-5 \right)+3\left( y-5 \right)\]
    \[=\left( y-5 \right)\left( y+3 \right)\]         


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