Question

18. (l + m)^2
(l - m)^2​

Answer 1

Answer:

Step-by-step explanation:

Using the identity: a² - b² = (a+b)(a-b)

(l+m)² - (l-m)²

= [(l+m)+(l-m)]×[(l+m)-(l-m)]

= [l+m+l-m]×[l+m-l+m]

= [2l]×[2m]

=4lm

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Answer 2

Answer:

(l+m)²(l-m)²=l^4+m^4-2l²m²

Step-by-step explanation:

Given that,

(l+m)²(l-m)²

as we know that,

(a+b)²=a²+b²+2ab

& (a-b)²=a²+b²-2ab

here,a=l & b=m

now,

(l+m)²(l-m)²=(l²+m²+2lm)(l²+m²-2lm)

⇒l^4+l²m²-2l³m+m²l²+m^4-2lm³+2l³m+2lm³-4l²m²      (∵by multiplying)

⇒l^4+m^4+2m²l²-4l²m²         (∵By cancelling)

⇒l^4+m^4-2l²m²

∴(l+m)²(l-m)²=l^4+m^4-2l²m²

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