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If mm and nn are integers such that (2)1934429m8n=3n16m(644)(\sqrt{2})^{19} 3^{4} 4^{2} 9^m8^n = 3^n 16^m (\sqrt[4]{64}) then mm is

Solution

✅ Correct Option: 4

Given equation: (2)19⋅34⋅42⋅9m⋅8n=3n⋅16m⋅(644)(\sqrt{2})^{19} \cdot 3^{4} \cdot 4^{2} \cdot 9^m \cdot 8^n = 3^n \cdot 16^m \cdot (\sqrt[4]{64})


Convert everything to prime factors (2 and 3) because comparing powers of the same base is the easiest way to solve these equations.

Left side breakdown:

  • (2)19=(21/2)19=219/2(\sqrt{2})^{19} = (2^{1/2})^{19} = 2^{19/2}
  • 34=343^4 = 3^4
  • 42=(22)2=244^2 = (2^2)^2 = 2^4
  • 9m=(32)m=32m9^m = (3^2)^m = 3^{2m}
  • 8n=(23)n=23n8^n = (2^3)^n = 2^{3n}

Right side breakdown:

  • 3n=3n3^n = 3^n
  • 16m=(24)m=24m16^m = (2^4)^m = 2^{4m}
  • 644=641/4=(26)1/4=26/4=23/2\sqrt[4]{64} = 64^{1/4} = (2^6)^{1/4} = 2^{6/4} = 2^{3/2}

Combine powers of same bases:

Left side:

  • Powers of 2: 219/2⋅24⋅23n=219/2+4+3n=227/2+3n2^{19/2} \cdot 2^4 \cdot 2^{3n} = 2^{19/2 + 4 + 3n} = 2^{27/2 + 3n}
  • Powers of 3: 34⋅32m=34+2m3^4 \cdot 3^{2m} = 3^{4 + 2m}

Right side:

  • Powers of 2: 24m⋅23/2=24m+3/22^{4m} \cdot 2^{3/2} = 2^{4m + 3/2}
  • Powers of 3: 3n3^n

Since both sides must be equal, the powers of 2 must match and powers of 3 must match.

For powers of 2:

272+3n=4m+32\dfrac{27}{2} + 3n = 4m + \dfrac{3}{2} ... (1)

For powers of 3: 4+2m=n4 + 2m = n ... (2)


From equation (2): n=4+2mn = 4 + 2m

Substitute into equation (1):

272+3(4+2m)=4m+32\dfrac{27}{2} + 3(4 + 2m) = 4m + \dfrac{3}{2}

272+12+6m=4m+32\dfrac{27}{2} + 12 + 6m = 4m + \dfrac{3}{2}

272−32+12=4m−6m\dfrac{27}{2} - \dfrac{3}{2} + 12 = 4m - 6m

242+12=−2m\dfrac{24}{2} + 12 = -2m

12+12=−2m12 + 12 = -2m

24=−2m24 = -2m

m=−12m = -12


Verify: If m=−12m = -12, then n=4+2(−12)=−20n = 4 + 2(-12) = -20

Check equation (1):

272+3(−20)=4(−12)+32\dfrac{27}{2} + 3(-20) = 4(-12) + \dfrac{3}{2}

272−60=−48+32\dfrac{27}{2} - 60 = -48 + \dfrac{3}{2}

−932=−932\dfrac{-93}{2} = \dfrac{-93}{2} ✓

Therefore, m=−12m = -12

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