Question

"Question 15 Find and correct the errors in the statement: (a − 4) (a − 2) = a^2 − 8

Class 8 Factorisation Page 229"

Answer 1

Common errors we done by solving algebraical expression and equation:

 
Error 1
Coefficient 1 of a term is usually not written. So we often ignores that. But while adding like terms, we should include it in the sum.

 
Error 2
When we multiply the expression enclosed in a bracket by a constant (or a variable) outside, we usually applied the multiplication to first term only. This is wrong calculation. Each term of the expression has to be multiplied by the constant (or the variable).

 
Error 3
when we square a monomial, we usually ignored the   numerical coefficient. This is wrong method. The   numerical coefficient and each factor has to be squared.

 
Error 4
when we square a binomial, we usually do not apply the proper identity. This is wrong approach. The right identity should be used.

Error 5

While dividing a polynomial by a monomial, We usually don’t divide each term of  the polynomial in the numerator by the monomial in the denominator.

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Solution:

(a − 4) (a − 2) = a² − 8

LHS= (a - 4) (a - 2) 

=a² -2a-4a+8

=a² -6a+8

RHS = a² - 8

LHS≠ RHS

Correct statement 

(a - 4) (a - 2) =a² -6a+8

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Hope this will help you...