use suitable identity to find the product ( x + 4 )(x+10
Answers
Identity:
An identity is an equality which is true for all values of a variable in the equality.
(x + a) (x + b) = x²+(a + b) x + ab
In an identity the right hand side expression is called expanded form of the left hand side expression.
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Solution:
(i) Using identity,
[(x + a) (x + b) = x² + (a + b) x + ab]
In (x + 4) (x + 10),
a = 4 & b = 10
Now,
(x + 4) (x + 10)
= x² + (4 + 10)x + (4 × 10)
= x² + 14x+ 40
(ii) (x + 8) (x – 10)
Using identity,
[(x + a) (x + b) = x² + (a + b) x + ab]
Here, a = 8 & b = –10
(x + 8) (x – 10)
= x²+{8+(– 10)}x +{8×(– 10)}
= x² + (8 – 10)x – 80
= x² – 2x – 80
(iii) (3x + 4) (3x – 5)
Using identity,
[(x + a) (x + b) = x² + (a + b) x + ab]
Here, x = 3x , a = 4 & b = -5
(3x + 4) (3x – 5)
=(3x)²+{4 + (-5)}3x +{4×(-5)}
= 9x² + 3x(4 – 5) – 20
= 9x² – 3x – 20
(iv) (y² + 3/2) (y² – 3/2)
Using identity,
[ (x + y) (x –y) = x² – y²
]
Here, x = y² and y = 3/2
(y² + 3/2) (y² – 3/2)
= (y²)² – (3/2)2
= y4– 9/4
(v) (3 – 2x) (3 + 2x)
Using identity,
[(x + y) (x –y) = x² – y²
Here, x = 3 & y = 2x
(3 – 2x) (3 + 2x)
= 3² – (2x)²
=9– 4x²
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