使用网格来绘图(错误使用网格(第76行)X, Y, Z, C不能复杂)

I'm trying to plot this function but keep getting 'Error using mesh (line 76) X, Y, Z, and C cannot be complex'. I found another question that suggested the use of abs on the sqrt function but this does not give the desired output. The output given should look like thisI'm trying to plot this function but keep getti