To find the value of the expression \( 7x^2 + 9x - 3 \) when \( x = 3 \), we first substitute \( x \) with 3 in the expression.
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Substitute \( x \) with 3: \[ 7(3)^2 + 9(3) - 3 \]
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Calculate \( (3)^2 \): \[ 7 \cdot 9 + 9 \cdot 3 - 3 \]
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Now multiply: \[ 63 + 27 - 3 \]
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Add \( 63 \) and \( 27 \): \[ 90 - 3 \]
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Finally, subtract \( 3 \): \[ 87 \]
Thus, the value of the expression \( 7x^2 + 9x - 3 \) when \( x = 3 \) is \( \boxed{87} \).