MathML

<math>
    <mrow>
        <msup>
            <mfenced>
                <mrow>
                    <mi>a</mi>
                    <mo>+</mo>
                    <mi>b</mi>
                    </mrow>
                </mfenced>
            <mn>2</mn>
            </msup>
        </mrow>
    </math>
a + b 2 = a 2 + 2 a b + b 2