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Using the formula, find the cubes of the following expressions:

(a) [tex]\((a + 4)\)[/tex]

(b) [tex]\((a - 5)\)[/tex]

(c) [tex]\((2a + b)\)[/tex]

(d) [tex]\((3a - 2)\)[/tex]


Sagot :

Sure, let's find the cubes of the given expressions one by one.

### Part (a): Cube of [tex]\((a + 4)\)[/tex]
To find the cube of the expression [tex]\((a + 4)\)[/tex], we use the binomial expansion formula for cubes:
[tex]\[ (x + y)^3 = x^3 + 3x^2y + 3xy^2 + y^3 \][/tex]
Here, [tex]\(x = a\)[/tex] and [tex]\(y = 4\)[/tex].

Substituting these values into the formula:
[tex]\[ (a + 4)^3 = a^3 + 3(a^2)(4) + 3(a)(4^2) + 4^3 \][/tex]
[tex]\[ (a + 4)^3 = a^3 + 12a^2 + 48a + 64 \][/tex]

### Part (b): Cube of [tex]\((a - 5)\)[/tex]
Using the same binomial expansion formula, [tex]\((x + y)^3\)[/tex], for [tex]\((a - 5)\)[/tex]:
[tex]\[ x = a, \quad y = -5 \][/tex]

Substituting these values:
[tex]\[ (a - 5)^3 = a^3 + 3(a^2)(-5) + 3(a)(-5^2) + (-5)^3 \][/tex]
[tex]\[ (a - 5)^3 = a^3 - 15a^2 + 75a - 125 \][/tex]

### Part (e): Cube of [tex]\((2a + b)\)[/tex]
Now, we'll cube [tex]\((2a + b)\)[/tex]:
[tex]\[ x = 2a, \quad y = b \][/tex]

Substituting:
[tex]\[ (2a + b)^3 = (2a)^3 + 3(2a)^2(b) + 3(2a)(b^2) + b^3 \][/tex]
[tex]\[ = 8a^3 + 12a^2b + 6ab^2 + b^3 \][/tex]

### Part (f): Cube of [tex]\((3a - 2)\)[/tex]
Finally, we cube [tex]\((3a - 2)\)[/tex]:
[tex]\[ x = 3a, \quad y = -2 \][/tex]

Substituting:
[tex]\[ (3a - 2)^3 = (3a)^3 + 3(3a)^2(-2) + 3(3a)(-2)^2 + (-2)^3 \][/tex]
[tex]\[ = 27a^3 - 54a^2 + 36a - 8 \][/tex]

### Summary
The cubes of the given expressions are:

1. [tex]\((a + 4)^3\)[/tex] is:
[tex]\[ a^3 + 12a^2 + 48a + 64 \][/tex]
2. [tex]\((a - 5)^3\)[/tex] is:
[tex]\[ a^3 - 15a^2 + 75a - 125 \][/tex]
3. [tex]\((2a + b)^3\)[/tex] is:
[tex]\[ 8a^3 + 12a^2b + 6ab^2 + b^3 \][/tex]
4. [tex]\((3a - 2)^3\)[/tex] is:
[tex]\[ 27a^3 - 54a^2 + 36a - 8 \][/tex]