简约学术风数学公式手写体黑色背景背景素材

minimalist typography art, black and white color scheme, mathematical formulas and symbols, clear display of standard deviation calculation formulas: ∑(i=1 to n) (x_i - x?)^2 / (n-1) and s = √[∑(i=1 to n) (x_i - x?)^2 / (n-1)], modern sans-serif font, no background design, conveys mathematical and statistical concepts, clean and academic visual style