To multiply \(0.75\) by \(2.8 \times 10^{-5}\), follow these steps:
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Multiply the coefficients: \[ 0.75 \times 2.8 = 2.1 \]
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Keep the exponent: Since we are multiplying by a power of ten, the exponent remains the same: \[ 2.1 \times 10^{-5} \]
Putting this together, we get: \[ 0.75 \times 2.8 \times 10^{-5} = 2.1 \times 10^{-5} \]
Thus, the correct response is: 2.1×10−5 (2 point 1 times 10 to the negative 5 power).