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The CENTRE for EDUCATION in MATHEMATICS and CON
Problem of the Week
Problem C
Exponential Expressions
two expressions:
Expression 
A:72 ×7^(x)
Expression 
B:441 ×2^(y)
Et 
x and 
y are positive integers, find all ordered pairs 
(x,y) so that th Exprestion 
A is equal to the value of Expression 
B.

A=B

The CENTRE for EDUCATION in MATHEMATICS and CON\newlineProblem of the Week\newlineProblem C\newlineExponential Expressions\newlinetwo expressions:\newlineExpression A:72×7x A: 72 \times 7^{x} \newlineExpression B:441×2y B: 441 \times 2^{y} \newlineEt x x and y y are positive integers, find all ordered pairs (x,y) (x, y) so that th Exprestion A A is equal to the value of Expression B B .\newlineA=B A=B

Full solution

Q. The CENTRE for EDUCATION in MATHEMATICS and CON\newlineProblem of the Week\newlineProblem C\newlineExponential Expressions\newlinetwo expressions:\newlineExpression A:72×7x A: 72 \times 7^{x} \newlineExpression B:441×2y B: 441 \times 2^{y} \newlineEt x x and y y are positive integers, find all ordered pairs (x,y) (x, y) so that th Exprestion A A is equal to the value of Expression B B .\newlineA=B A=B
  1. Factor out common factors: First, simplify the coefficients by factoring out common factors. 441441 is 6363 squared, and 6363 is 99 times 77, so 441=9×7×7441 = 9 \times 7 \times 7. Now we have 72×7x=9×7×7×2y7^2 \times 7^{x} = 9 \times 7 \times 7 \times 2^{y}.
  2. Divide by 99: Divide both sides by 99 to simplify. 72÷9=872 \div 9 = 8. So we get 8×7x=7×7×2y8 \times 7^{x} = 7 \times 7 \times 2^{y}.
  3. Isolate 7x7^{x}: Now, divide both sides by 77 to isolate 7x7^{x} on one side. 8×7x1=7×2y.8 \times 7^{x-1} = 7 \times 2^{y}.
  4. Rewrite 88 as 232^3: We can see that 88 is 22 cubed, so we rewrite 88 as 232^3. Now we have 23×7(x1)=7×2y2^3 \times 7^{(x-1)} = 7 \times 2^y.
  5. Equate the exponents: Since the bases are now the same (22 and 77), we can equate the exponents. 3+(x1)=y3 + (x-1) = y and x1=1x-1 = 1. So we have two equations: 3+x1=y3 + x - 1 = y and x1=1x - 1 = 1.
  6. Solve for x: Solve the second equation for x. x1=1x - 1 = 1 gives us x=2x = 2.
  7. Substitute xx into yy: Substitute x=2x = 2 into the first equation to find yy. 3+21=y3 + 2 - 1 = y gives us y=4y = 4.
  8. Check the solution: Check if the ordered pair (x,y)=(2,4)(x,y) = (2,4) satisfies the original equation. 72×7272 \times 7^{2} should equal 441×24441 \times 2^{4}. Calculate both sides: 72×49=352872 \times 49 = 3528 and 441×16=7056441 \times 16 = 7056. Oops, there's a mistake here, the calculations don't match.

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