AlphaBlend will not compile

[aewarnick]

::AlphaBlend(a::hdc, xOffset, yOffset,
drawLocation->right-drawLocation->left, drawLocation->bottom-drawLocation->top,
invalDC, 0, 0,
drawLocation->right-drawLocation->left, drawLocation->bottom-drawLocation->top, bf);
error message:
[Linker Error] Unresolved external 'AlphaBlend' referenced from D:\MY DOCUMENTS\C++ PROJECTS\GAME\MAIN.OBJ