Fractional Bernoulli polynomials optimization approach for nonlinear system of time fractional PDEs in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si10.svg"> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>2</mml:mn> <mml:mo linebreak="goodbreak">+</mml:mo> <mml:mn>1</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> -dimensional