Can't rotate a QImage to 45 degrees by Y Axis

bool func1()
{
    QImage image(3840, 2160, QImage::Format_ARGB32_Premultiplied);
    image.fill(Qt::red);

    QTransform t;
    t.translate(image.width() / 2.0, image.height() / 2.0);
    t.rotate(-45, Qt::YAxis);
    t.translate(-image.width() / 2.0, -image.height() / 2.0);
    image = image.transformed(t);

    return image.save("/tmp/func1.png");
}

bool func2()
{
    QImage image(3840, 2160, QImage::Format_ARGB32_Premultiplied);
    image.fill(Qt::red);

    QTransform t;
    t.translate(image.width() / 2.0, image.height() / 2.0);

    qreal b = qDegreesToRadians(-45);
    qreal sina = qSin(b);
    qreal cosa = qCos(b);
    QTransform tmp(cosa, 0, -sina / image.width(), // There is "-sina / 1024" in QTransform::rotate
                   0, 1, 0,
                   0, 0, 1);

    t = tmp * t;
    t.translate(-image.width() / 2.0, -image.height() / 2.0);
    image = image.transformed(t);

    return image.save("/tmp/func2.png");
}