Elementary Algebra
- If a + b + 1 = 0, then the value of (a3 + b3 + 1 – 3ab) is
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As we know from the formula,
A3 + B3 + C3 = ( A + B + C) (A2 + B2 + C2 – AB – BC – CA) + 3ABC
If A + B + C = 0 then,
A3 + B3 + C3 = 0 x (A2 + B2 + B2 – AB – BC – CA) + 3ABC
A3 + B3 + C3 = 0 + 3ABC
A3 + B3 + C3 - 3ABC= 0Correct Option: B
As we know from the formula,
A3 + B3 + C3 = ( A + B + C) (A2 + B2 + C2 – AB – BC – CA) + 3ABC
If A + B + C = 0 then,
A3 + B3 + C3 = 0 x (A2 + B2 + B2 – AB – BC – CA) + 3ABC
A3 + B3 + C3 = 0 + 3ABC
A3 + B3 + C3 - 3ABC= 0
As we know that from given question,
A = a, B = b and C = 1, Put these value in above equation, we will get
a3 + b3 + 13 - 3 x a x b x 1 = 0
a3 + b3 + 1 - 3ab = 0
- Two candidates attempt to solved a quadratic equation of from x2 + px + q = 0. One starts with a wrong value of p and finds the roots to be 2 and 6. Other starts with a wrong value of q and find the root to be 2 and -9. Find the correct roots and equation ?
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When p is wrong i.e., -b/a = (α + β) is wrong but c/a =(αβ) is correct.
Then αβ = c/a = 2 x 6 = 12 ....(i)
Again, when q is wrong i.e.,c/a = (α.β ) is wrong but -b/a = α+β is correct.
Then, -b/a = α+β= 2 + (-9) = -7Correct Option: C
When p is wrong i.e., -b/a = (α + β) is wrong but c/a =(αβ) is correct.
Then αβ = c/a = 2 x 6 = 12 ....(i)
Again, when q is wrong i.e.,c/a = (α.β ) is wrong but -b/a = α+β is correct.
Then, -b/a = α+β= 2 + (-9) = -7
So, the required correct quadratic equations is
x2 -(α + β)x + α.β=0
⇒ x2 - (-7)x + 12 = 0
⇒ x2 + 7x + 12 = 0
and correct roots this equations are -3, -4.
- If the cost of 2 apples, 3 oranges and a pear is Rs.62 and the cost of 5 apples, 6 oranges and 4 pears is Rs. 120, then find the cost of 3 apples, 3 oranges and 3 pears ?
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Let the cost of each apple,orange nd pear be Rs.x,y and z, respectively.Then,
2x + 3y + z = 62 ...(i)
5x + 6y + 4z = 20 ...(ii)
Correct Option: C
Let the cost of each apple,orange nd pear be Rs.x,y and z, respectively.Then,
2x + 3y + z = 62 ...(i)
5x + 6y + 4z = 20 ...(ii)
On subtracting Eq.(i)from Eq.(ii), we get
3x + 3y + 3z = 58
So, the cost of 3 apple,3 oranges and 3 pears is Rs. 58.