Question

21) By using suitable identity, find the value of:
(a) (-6)³ + 13³ + (-7)³. (b) (-21)³ + (28)³​

Answer 1

Answer:

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Answer 2

Answer:

(-6)³+(13)³+(-7)³=1638

(-21)³+(28)³=343

Step-by-step explanation:

(-6)³+(13)³+(-7)³=1638

Explanation

As we all. Know

X³+y³+z³=3xyz(but only in one condition if

x+y+z=0 and (-6)+13+(-7)=0 which mean we can use this formulla)

So,

x³+y³+z³=3xyz

=(-6)³+(13)³+(-7)³=3(-6)(13)(-7)

Hence(-6)³+(13)³+(-7)³=1638

Now

(-21)³+(28)³= 343

explanation

As we know

a³+b³=a³+3a²b+3ab²+b³

(-21)³+(28)³=(-21)³+3(-21)²(28)+3(-21)(28)²+(28)³

Hence (-21)³+(28)³=343