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Re: If x * = x^2 + 4, which of the following is equivalent to
[#permalink]
21 Dec 2017, 09:18
2
Hi,
I would like to mention an error that u post above. ie u wrote 2*=2^2+2=4 .it is wrong.but agreeing with ur final answer. 2*=2^2+4=8 and the only number to the * which leads to 8 is -2.thus the answer is option A.
Re: If x * = x^2 + 4, which of the following is equivalent to
[#permalink]
25 Aug 2022, 10:07
1
Given that x∗=x2+4 and we need to find the value of 2∗
To find 2∗ we need to compare what is before * in 2∗ and x∗
=> We need to substitute x with 2 in x∗=x2+4 to get the value of 2∗
=> 2∗=22+4 = 4 + 4 = 8
Now, the answer choices are also given in terms of * so we need to solve for each answer choice and check which one will be equal to 8. Let's solve it using two methods
Method 1: Algebra
If we take a closer look at x∗=x2+4 then we realize that x* is nothing but square of x + 4 = 8 (in case of 2*) => Square of x = 8 - 4 = 4 => x = ± √4 = ±2 => x can be -2 also
So, Answer will be A
Method 2: Substitution
Lets take each option choice and check which one equates to 8
A)(−2)∗=(−2)2+4 = 4 + 4 = 8 => POSSIBLE In exam we don't need to solve further but I am solving to complete the solution
B)0∗=02+4 = 0 + 4 = 4 => NOT POSSIBLE
C)4∗=42+4 = 16 + 4 = 20 => NOT POSSIBLE
D)6∗=62+4 = 36 + 4 = 40 => NOT POSSIBLE
E)8∗=82+4 = 64 + 4 = 68 => NOT POSSIBLE
So, Answer will be A Hope it helps!
Watch the following video to learn the Basics of Functions and Custom Characters
gmatclubot
Re: If x * = x^2 + 4, which of the following is equivalent to [#permalink]